Browsing by Author "Gous, Robert Mervyn."

Now showing 1 - 20 of 45

Biological and economic response of laying hens to dietary isoleucine, methionine, lysine and energy.
(1980) Griessel, Munro.; Gous, Robert Mervyn.
No abstract available.
Biological and economic response of laying hens to dietary lysine and energy contents during peak and late production periods.
(2001) Netshipale, Justice A.; Slippers, S. C.; Gous, Robert Mervyn.
The effect of dietary energy and amino acid contents during the peak of production of laying hens has been well investigated, but little is known about the late production period. In most of the previous studies the focus has been on improving the performance of laying hens with little, if any, consideration of the costs of achieving the maximum performance. The aim of the present study was, (i) to investigate the effect of dietary lysine and energy contents on the performance of laying hens (ii) to find out whether young (30-40 weeks) and old hens (60-70 weeks) perform the same at given dietary lysine and energy contents, and (iii) to determine the differences in income and costs generated by young and old laying hens. It was hypothesised that young laying hens will perform better and yield more income at given dietary lysine and energy contents than old hens. Two experiments were conducted, during peak (30-40 weeks) and late production period (60-70 weeks) with 240 Lohmann Brown laying hens. For the first experiment, four basal diets, which were a combination of two lysine and two energy levels, were supplied by a commercial feed company. These basal diets were blended with one another in different proportions to produce 15 experimental diets, resulting in five lysine and three energy levels. In the second experiment a feed formulating program (WINFEED) was used to formulate four basal diets with lysine and energy levels that were intended to be close to those used in experiment 1. Due to a blending error, diets with three lysine and five energy levels were produced. This error made it impossible to compare the results of the early and late production period, as originally intended. During both experiments, each bird was allocated between 1.4 and 2 kg feed at the start of each week, when feed was weighed. Egg numbers were recorded daily, at the same time each day, and mean egg weight was recorded by weighing eggs on three consecutive days during each week. It was found that the dietary lysine contents used in both experiments were sufficient to support maximum egg production and that resulted in no statistically significant differences (p>0.05) between treatments being observed in egg production traits (rate of lay, egg weight and egg output). A significant effect of dietary energy content was observed on feed intake, which confirmed that dietary energy content had a significant but indirect effect on egg production, through its effect on the amount of dietary lysine consumed. Older birds were found to be producing 21 g less egg material per day than younger hens, at a given (comparable) dietary lysine and energy content. This result confirmed that older hens require more nutrients to produce a given quantity of egg material. Since the performance of old hens was lower at a given dietary lysine and energy content, the profit generated was also lower. Younger hens generated numerically higher returns than the predicted returns for older hens, at any given combination of dietary lysine and energy tested. However, it was not possible to verify the results statistically, because the expected responses used for older hens were predicted from the results of young hens. In both ages (over the range of dietary lysine and energy contents used) highest returns were realised with the combination of lowest dietary energy and all lysine contents. The effect of a change in egg price was felt more with hens producing heavier egg at both ages, with young hens being more affected than the old hens. The results from these experiments give some indication on trends of returns for hens of both ages, although the economic optimum combinations of dietary energy and lysine could not be predicted (because of the dietary lysine and energy contents used, that were all sufficient to support maximum egg production).
The biological and economic responses of growing pigs to nutrient density.
(1999) Nelson, Lyska Michelle.; Gous, Robert Mervyn.; Ferguson, Neil Stuart.
No abstract available.
The calcium requirement of commercial layer pullets in the pre-laying period.
(2003) Themeli, Lufuluvhi Reginald.; Gous, Robert Mervyn.
Specifications for the amount of calcium to be included in feeds for pullets and laying hens vary considerably in the scientific literature. Much of this variation is due to the fact that genetic selection has changed the growth rate, age at sexual maturity and potential egg production of laying hens over the years, and these changes will continue in the future. Husbandry techniques have also changed, so that pullets are now sometimes encouraged to start producing eggs at an earlier age with the use of appropriate lighting programmes. The supply of calcium to pullets in the pre-laying period depends critically on the age at which the pullets reach maturity and start to lay eggs, as pullets should be given an opportunity to deposit calcium in their medullary bone just before laying commences. The difficulty is knowing how much calcium should be included in the feed before sexual maturity, and for how long before this event a higher calcium content should be included, in order to minimise problems associated with mineral deficiencies and excesses during the laying period. The aim of the present study was to determine whether, by offering pullets a choice of two feeds varying in calcium content, the choice they made in the period leading up to sexual maturity could be used to determine the amount of calcium that should be fed to them during this period. Two experiments were conducted with Hyline pullets: in the first, 384 pullets were used, starting at 14 weeks of age, and in the second, 144 birds were used, starting at 10 weeks of age. In both experiments, equal numbers of Hyline Brown and Hyline Silver pullets were used. The first experiment consisted of four dietary treatments: Two basal diets were formulated to contain high (30 g calcium/kg) and low (8 g calcium/kg) calcium contents, with all other nutrients being the same. These two basal diets were fed alone and as a 1:1 blend to produce an intermediate calcium diet (19 g calcium/kg). The fourth treatment consisted of the low calcium basal and limestone grit as a choice diet. At 18 weeks of age six pullets from each treatment were killed for analysis of tibia breaking strength and 144 of these pullets (72 Silver and 72 Brown) were selected randomly and kept on the same treatment as before, but individually so that age at sexual maturity could be determined. There was no significant difference observed in age at sexual maturity or mortality, but pullets that were on the low calcium feed consumed significantly more feed and consequently, attained higher body weight gain than the other treatments. The opposite occurred for pullets that were on the high calcium diet. There was no significant effect of dietary calcium content on tibia breaking strength at 17 weeks. For the second experiment, pullets (n = 144) were reared on a lighting regime of 8L:16D to 10, 14 or 18 weeks, at which ages the photoperiod was increased to 14 hours. This had the effect of altering the age at sexual maturity, so that the effects of age and attainment of sexual maturity could be separated when determining the choice made by pullets in the amount of calcium consumed in the pre-laying period. In all cases, pullets increased their intake of calcium approximately two weeks before attaining sexual maturity, this increase being independent of the age of the pullets at the time. The study revealed that commercial laying-type pullets increase their intake of calcium, when given the opportunity to do so, approximately two weeks prior to the onset of lay. Where they do not have a choice between two sources of calcium this increased requirement for calcium causes pullets on low calcium feeds to increase their intake of feed and consequently simultaneously increase the intake of all nutrients other than calcium, resulting in an increased body weight. Where birds are fed a high calcium feed only, food intake does not increase to the same extent during this period, but the increase observed is likely to be to satisfy the increased demand for nutrients other than calcium in this pre-laying period. On the basis of the choices made by pullets in this study, these birds should be reared on low calcium feeds until two weeks before the onset of lay, at which stage the calcium should be increased to enable the pullets to deposit calcium in their medullary bone in preparation for the increased demand for calcium in the laying period.
Choice feeding as a method of meeting the changing protein requirements of broilers during their growing period.
(2005) Abdella, Mohamed Salih.; Gous, Robert Mervyn.
Broiler production is an important animal production enterprise with potential to make high returns. Increasing feed efficiency and early body weight gain has always been a top priority in the broiler industry. The general objective of broiler nutrition is to maximise production performance and profitability . Nutrition is of major importance in raising chicken, and feed is a major input in poultry production systems, accounting for over 60% of total production costs in commercial poultry sector Renkema (1992). The cost of feed is therefore often a constraint especially in developing countries. For instance, Onyenokwe (1994) observed that high cost of feed ingredients in many African countries has caused many poultry farmers to abandon the industry. The continued rise in feed prices is due to competition for some of the ingredients with human e.g. sorghum, wheat and maize. Broiler farmers are therefore forced to use combinations of feed ingredients of low cost to obtain savings and avoid any further loss of profits. It is therefore important to give special attention to feed and feeding since the rate of feed consumption increases rapidly with advancing age of the birds and good nutrition is reflected in the bird's performance and its products. The profitability of a broiler enterprise depends on the efficient conversion of feed to meat. Broilers have the ability to convert the feeds into meat with a high efficiency. For instance Morris and Njuru (1990) reported that broilers have much higher daily rates of protein deposition than layer chicken strains. This implies that fast-growing strains would require greater daily protein intakes than slow-growing ones. In the past, the major criteria for assessing the performance of broilers has been growth rate and feed conversion ratio (FeR). Diet specifications and feeding programmes have been aimed at maximising these two parameters whereby overall flock performance is calculated based on the total weight of chicken produced from total feed deliveries. With the new developments in understanding of nutritional factors affecting broiler growth and carcass composition, it is now possible to apply sophisticated and yet efficient approaches to feeding broilers.
The constraining effect of feed bulk on the voluntary feed intake of laying hens.
(2004) Moore, Martina Louise.; Gous, Robert Mervyn.
1. Two experiments were designed to determine a suitable method of measuring and predicting feed bulk, such that this could be used to predict when the feed intake of a laying hen would be constrained by feed bulk. 2. In the first trial the diluents used were cellulose, plasterer's sand, sunflower husks, sawdust and vermiculite. These were included at 100, 250 and 500 g/kg into a commercial layer feed which was used as the basal feed. The trial was divided into three phases of 21 days each. After each phase, either the diluent fed was changed, or the inclusion level of the diluent was changed. 3. It was observed that as the water-holding capacity (WHC) of the feed increased, the feed intake decreased. The scaled feed intake (SFI) of the hens was fitted to the reciprocal of the WHC to give the relationship; SFI (g/kg body weight) = 313.6 (±8.9) x 1/WHC. This regression was the best fit and represents the maximum amount of feed that the laying hen can consume when the constraint measured is the reciprocal of WHC. 4. Trial 2 identifies the physical characteristics of the feed that best describe the bulkiness of the feed, and also determined the extent, and the rate at which, the laying hen can adapt to feeds that are high in bulk. The five diluents that were used were wheat bran, river sand, potter's clay, unexpanded polystyrene and sawdust, and the inclusion rates were 50, 100 and 150 g/kg. The hens were fed the feeds for six weeks. The equation from Trial 1 was fitted to the data from Trial 2 and few treatments were found to be constraining. 5. The constraining feeds from both trials and Williams (1993) were combined to obtain a more accurate assessment of the relationship between the SFI and the reciprocal of WHC. This relationship was represented by the equation; SFI (g/kg body weight) = 301.4 (±8.9) x 1/WHC. 6. The prediction of the effect of feed bulk on the voluntary feed intake of the hen is an important aspect for accurately predicting the feed intakes of the hen and formulating a "perfect" diet. The variation in constrained intakes was not accurately predicted by the WHC of the feed, although this measure of bulkiness was considerably better than any of the other measures applied.
A description of the genotype of pigs using simulation modelling.
(1996) Ferguson, Neil Stuart.; Gous, Robert Mervyn.
No abstract available.
Economic optimum nutrition of growing pigs.
(2022) Pennicott, Chantel Gwen.; Gous, Robert Mervyn.
In two trials, a total of 504 boars and 504 gilts were used to determine the most profitable feeding strategy for the Topigs TN60 strain under current economic circumstances, using margin over feed cost as the objective function. The trials started when the pigs were 10 weeks old and were terminated after a 12-week trial period in each case. In the first trial the EFG Pig Model and Optimiser was used to assess the current feeding strategy used on the Baynesfield Estate, and to determine how the optimum strategy might change under different economic scenarios. An added objective was to evaluate the Pig Growth Model by comparing the predictions made by the model with the actual outcomes of the trial. Significant differences in gains, feed intake and carcass parameters were measured across sexes and feed treatments, and hence margin over feed cost, under the different economic scenarios applied. The Growth Model accurately predicted the optimum feeding strategy although the predicted feed intakes were marginally lower than those measured in the trial. The response to a series of feeds differing in balanced protein was measured in the second trial, the main objective being to develop equations that would describe the response of boars and gilts of this strain to dietary protein. These equations could then be used in the future to calculate the optimum economic level of dietary protein as economic circumstances on the farm changed. The results of both the simulation exercise and the trial provided strong evidence that the optimum economic level of dietary protein differs for gilts and boars, and that this difference widens as profitability in the enterprise is reduced, either through an increase in the cost of feed ingredients or when pork prices decline. Uniformity in body and carcass weight was increased with dietary protein content. The results of both trials provide convincing evidence that gilts and boars should be reared separately, and fed different dietary protein levels, if margin over feed cost is to be maximized, and that the economic optimum feeding strategy is not static but varies with economic circumstances.
Effect of alternatives to antibiotic growth promoters on broiler performance.
(2006) Mosoeunyane, Nthoto V.; Gous, Robert Mervyn.
No abstract available.
The effect of dietary protein and energy on feed intake and performance of laying hens.
(2005) Nkukwana, Thobela T.; Gous, Robert Mervyn.
This study was designed to devise a method by which the optimum combination of dietary energy and protein could be found that maximises the margin over feeding cost in an egg production enterprise. It was necessary to be able to predict feeding costs and revenue associated with the use of a wide range of feeds varying in protein and energy. To this end, two experiments were conducted using 256 Lohmann (128 White and 128 Brown) in the first, and 1296 Hy-line Brown laying birds in the second trial, that were 33 and 38 weeks old at the beginning of the two trials. Using the WinFeed 1.1 (1996) feed formulation programme, four basal (corner) feeds were formulated in both experiments, from which four protein and four energy contents (16 feeds) were produced in the first experiment, and six protein and three energy contents ( 18 feeds) were used in the second. Each feed was given to three replicates of 16 birds in the first trial, and to three replicates of 24 birds in the second. The trials each lasted ten weeks, and the data collected included food intake, change in body weight, egg weight and rate of laying. Using the results from these two experiments and from previously published research, the effects of dietary protein and energy on food intake were predicted independently, and these predictions were then used to determine the cost of feeding. Similarly, egg weight and rate of lay were predicted independently for changes in dietary protein and energy, from which the revenue could be calculated over the range of energy and protein contents. It is understood that a more integrated approach would be more accurate for this purpose, but such an approach was beyond the scope of this investigation. The use of contour plots based on regression analyses of the estimated income-minus-feeding cost on changes in dietary protein and energy enabled evaluations to be made of the effect on profitability of changes in egg price and maize price. And it was deduced that under conditions in which the maize price is high, maximum profitability is achieved with high energy and high protein content, irrespective of the price paid for eggs. When the maize price is reduced, the combination of protein and energy that yields the highest return over feed cost changes to low protein and low energy feeds. This change is defensible on the grounds that the price of high-density feeds does not change as much as that of low-density feeds when the maize price is lowered, whereas production, and hence returns, remains the same, hence the low density feeds yield higher returns under such circumstances. The method applied in this study appears to be a useful tool for decision-making by egg producers and nutritionists.
The effect of group size and floor-space allowance on the efficiency of lysine utilisation by growing pigs.
(2005) Theeruth, Bianca Karen.; Gous, Robert Mervyn.
Two experiments were conducted for this thesis, to determine whether an animal should be fed to its genetic potential in spite of this not being achievable due to an on-farm constraint. The first experiment was designed to compare the response of pigs housed either individually or in groups to a range of feeds limiting in lysine between 40 and 85 kg live weight. Two hundred and eighty-eight entire male Large White x Landrace pigs were used. The experiment was divided into two growth periods, i.e. from 40 to 60 kg and from 60 to 85 kg. In each period, pigs were subjected to feed containing one of four dietary lysine concentrations. In Period 1, the lysine concentrations were 11.03 (L1); 9.54 (L2); 8.00 (L3) and 6.51 (L4) g/kg, while in Period 2 these were 7.82 (T1); 6.71 (T2); 5.55 (T3) and 4.40 (T4) g/kg. Pigs fed an L1, L2, L3 or L4 diet in Period 1 were fed a T1, T2, T3 and T4 diet in Period 2, respectively. Three buildings provided the following group sizes and floor-space allowances: House 1 contained eight pigs per pen at 1.94 m2/pig; House 2 contained four or eight pigs per pen at 1.72 or 0.86 m2/pig; and House 3 contained one pig per pen at 1.72 m2/pig. The individually-housed pigs were divided into three feeding levels, i.e. ad libitum, or pair-fed so that feed intakes would match those of ad libitum-fed pigs housed in groups of either 4 (restricted-4) or 8 (restricted-8) pigs per pen in House 2. For all group sizes, feed intake increased linearly as the dietary lysine content increased. However, this increase was significantly lower for 8, when compared with 1 and 4 pigs per pen. The linear increase in feed conversion efficiency with dietary lysine content was similar for all group sizes. However, at any dietary lysine concentration, pigs housed in groups of 8 had significantly higher efficiencies than the pigs housed individually or in groups of 4. Average daily gain increased linearly as lysine intake increased, this increase being the same for all group sizes. However, pigs in smaller groups grew significantly faster than those in larger group sizes for any lysine intake. Protein and lysine retention were unaffected by group size, increasing linearly as lysine intake increased. The efficiency of lysine utilisation (0.45) was not impaired by group size. The pair-fed pigs housed individually (restricted-4 and -8) consumed significantly less feed than the individually-housed pigs fed ad libitum, and this was reflected in their average daily gains, which increased linearly as lysine intake increased, but with the restricted-8 growing significantly slower than the ad libitum or restricted-4 pigs. In all three treatments feed conversion efficiency increased linearly with dietary lysine content, although the restricted-4 and -8 had significantly higher efficiencies than the ad libitum-fed pigs at any dietary lysine content. Protein and lysine retentions were unaffected by feeding level and increased significantly with lysine intake. However, at any lysine intake the restricted-8 pigs had a significantly lower efficiency of lysine utilisation than the ad libitum or restricted-4 pigs. The pigs with floor-space allowances of 0.86 and 1.94 m2/pig consumed significantly less and grew slower than the pigs with floor-space allowances of 1.72 m2/pig at any dietary lysine content. Feed conversion efficiency was unaffected by floor-space allowance and increased significantly with dietary lysine content. Similarly, protein and lysine retentions were unaffected by floor-space allowance and increased linearly as lysine intake increased. The efficiency of lysine utilisation (0.45) remained unaffected by floorspace allowance. It was concluded that when animals are socially stressed, feeding according to the requirement for maximum protein growth produces the best biological performance and carcass composition, with the corollary that, if profitability and biological efficiency is to be maximised, pigs housed in stressful conditions, or those whose future performance is predicted to be below potential because of external stressors, should not be given feed of an inferior quality. The second experiment was designed to determine the extent to which grouping or floorspace allowance would alter the nutrient content of feed chosen by pigs given a choice of two feeds differing in protein: energy ratio between 40 to 85 kg live weight. Three hundred and eighteen entire male Large White x Landrace pigs were used. Two buildings provided the following group sizes and floor-space allowances: House 1 contained nine and eighteen pigs per pen at 1.72 or 0.86 m2/pig; House 2 contained four, nine and fourteen pigs per pen at 1.72; 0.86 or 0.49 m2/pig. Animals were given simultaneous ad libitum access to a high (236 g protein/kg as fed) and a low crude protein feed (115 g protein/kg as fed) in two hardened plastic self-feeder bins placed side-by-side. A training period of six days was used prior to the start of the trial, during which the two feeds were alternated daily. The reduction in the proportion of high protein feed chosen over time was significantly higher for the groups of four and eight, in comparison to the groups of nine and eighteen, contrasting with the steady increase for the groups of fourteen pigs. Similarly, the significant increase for pigs with floor-space allowances of 0.49 m2/pig differed from the significant decrease for pigs with floor-space allowances of 0.86 and 1.72m2/pig. Pigs housed in larger group sizes and smaller floor-space allowances consumed significantly less and grew slower than pigs housed in smaller group sizes and larger floorspace allowances. However, the feed conversion efficiency remained unaffected by group size and floor-space allowance. The non-significant effect on protein retention with increasing group size contrasted with the significant increase associated with increasing floor-space allowance. The results of the two studies were compared to determine whether pigs chose differently depending on the degree of stress and the implication of this choice. Average daily gain was significantly reduced as the group size increased for pigs fed a fixed lysine content and choice-fed. However, this reduction was less severe with choice-feeding than when feeding a fixed lysine content. Increasing the group size significantly reduced the feed intake in pigs fed a fixed lysine content only. The efficiency of protein utilisation remained unaffected as the group size increased for the pigs fed a fixed lysine content. However, at any group size pigs fed lower lysine contents had higher efficiencies than pigs fed higher lysine contents. On the contrary, increasing the group size significantly increased the efficiency of protein utilisation in choice-fed pigs. The average daily gain and feed intake was significantly improved as the floor-space allowance increased but was similar for pigs fed a fixed lysine content and choice-fed. Although the efficiency of protein utilisation remained unaffected by increasing the floor-space allowance for the pigs fed a fixed lysine content and pair-fed, at any floor-space allowance pigs fed higher lysine contents had higher efficiencies than pigs fed lower lysine contents. The results indicate that providing socially stressed pigs a choice between an appropriate pair of feeds differing in protein: energy ratio, does not overcome the reduction in potential growth, but does result in performance similar to that of pigs fed a fixed lysine content. It was concluded that the social stress of grouping or floor-space allowance has no influence on the ability of the animal to select an appropriate dietary combination allowing the expression of potential growth within the constraint(s) of the production system.
The effect of photoperiod and feeding time on broiler breeder eggshell quality and oviposition time.
(2004) Backhouse, Dean.; Gous, Robert Mervyn.
This study was conducted to determine the effect of photoperiod and feeding time on oviposition time and eggshell quality of broiler breeders. Five experiments were conducted in total. The effect of photoperiod on oviposition time was tested in Experiments 1 and 2. Experiment 1 involved 3200 33-week old broiler breeder hens housed in floor pens and subjected to photoperiods of 10, 11, 12, 13, 14 or 16 h. Experiment 2 used 120 37-week old broiler breeders, housed in individual cages in each of two light-proof rooms; one room on 8-h and the other on 16-h photoperiods. Birds in Experiment 1 were also used to determine the effect of photoperiod on eggshell quality, although they were 52 weeks of age when shell quality was assessed. The effect of feeding time on the aforementioned parameters was tested in three experiments. Experiment 3 involved 432 24-week old broiler breeders housed in individual cages and 'subjected to a 14-h photoperiod from 07.00 to 21.00. The birds were fed at 07.30,09.30, 11.30, 13.30 or 15.30. In one further treatment, birds were fed half the daily feed allocation at 07.30 and half at 15.30. Experiment 4 made use of 800 57-week old broiler breeder females housed on litter floor pens and subjected to a 14-h photoperiod from 05.00 to 19.00. The birds were fed at 07.30, 10.00, 13.00 or 15.30. In Experiment 5, 240 35-week old broiler breeder females were subjected to a 16-h photoperiod from 07.00 to 23.00. The feeding times tested in Experiment 5 were 07.30, 10.00, 13.00 and 15.30. Mean oviposition time was delayed relative to dawn by approximately 0.5h for each I-h increase in photoperiod up to 14 h, but was similar for 14 and 16-h photoperiods. The time when half a day's eggs were laid was also delayed relative to dawn by approximately 0.5 h for each I-h increase in photoperiod, although this trend continued through to 16 h. The rate of change in mean oviposition time for each I-h increase in ≤14-h photoperiod was similar to that reported for early and modern egg-type hybrids, but, compared with modern genotypes, time of lay itself was 1 h later than white-egg and 2.5 h later than brown-egg hybrids. At photoperiods ≤12.25 h, the number of eggs laid before dawn increased by 4.5% for each 1-h reduction in daylength. Egg weight increased by 0.31 g, shell weight decreased by 30 mg, and shell thickness index decreased by 0.57 mg/cm2 for each 1-h increase in photoperiod. Changes in egg weight and eggshell thickness index might be overstated because eggs were collected at the same chronological time. In spite of this, the effect of time of egg-laying within the day was minimal in comparison, and did not negate the conclusion that egg weight increases, and shell weight and thickness index decrease with lengthening photoperiods. The effect of photoperiod on eggshell quality was not due to differences in the rate of lay between treatments. Shell weight was unaffected by time of lay. Mean eggshell thickness was increased significantly by 3.5 µm (approximately 1 %) per hour delay in feeding time when hens were housed in individual cages. However, eggshell thickness was not significantly affected by feeding time when birds were housed on litter floors. Mean oviposition time was delayed relative to lights-on by 5 min per hour delay in feeding time. Egg weight was not significantly affected by feeding time, suggesting that differences in shell thickness and oviposition times were not due to increased transit times through the oviduct. Data presented in this thesis suggest that the current commercial practice of subjecting broiler breeder flocks to photoperiods that are in excess of the photoperiod required for maximum egg production is questionable. Apart from being unnecessary and costly, providing broiler breeders with excessively long photoperiods may be a cause of depressed eggshell thickness with consequential low hatchability. Eggshell quality can be improved by delaying the time of feeding, although improvements may only be marginal in broiler breeder flocks that are housed on litter floors. However, delaying the time of feeding may cause a delay in oviposition times. Producers who wish to implement delayed feeding should thus consider the management implications of eggs being laid later in the day.
The effects of excess dietary crude protein on the efficiency of utilization of protein by broiler chickens.
(2002) Swatson, Harry Kofi.; Gous, Robert Mervyn.
No abstract available.
The effects of nutritional management on behaviour in thoroughbred racehorses.
(2007) Hackland, Jean.; Young, Marion Belinda.; Gous, Robert Mervyn.
This dissertation is the product of two behaviour studies and an in vitro fermentation trial. Both behaviour studies were conducted at the Ashburton Racehorse-Training Centre in Ashburton, near Pietermaritzburg in KwaZulu- Natal. The first behaviour study evaluated differences in behaviours obtained through feeding either twice or four times daily. This trial showed (P
Evaluating a selection index for improving body weight and egg production in a simulated population of broilers.
(2009) Tempest, Justine Claire.; Gous, Robert Mervyn.
The most successful method used for improving the growth rate of broilers is genetic selection. Improvements in nutrition, housing and disease resistance have been impressive, yet genetic selection is purported to have contributed the majority of the tremendous increase in growth rate that has taken place over the past 50 years (McKay, 2008). Many selection strategies are available, but not all are suitable, as the choice is dependent on the objective of the breeder. Selection strategies are bound to change over time as different traits become more important, and this has been the case in the broiler industry: focus was initially placed predominantly on growth rate, but the negative genetic correlation that exists between growth rate and reproductive and liveability traits has forced breeders to change their position, especially as growth rate has almost reached its upper limit and reproductive traits lag behind. This has resulted in a change from single trait to multiple trait selection. In the exercise reported here, four selection strategies commonly used for single trait selection, namely individual, between family, within family and family-index selection, were applied to a simulated broiler population using the Monte Carlo method of simulation, and constructed with the use of genetic parameters obtained from the literature. Theoretical and simulated methods of the four selection strategies were compared. A fifth selection strategy, index selection, was applied to represent multiple trait selection. The relative merit of each selection procedure was then compared, as well as the results obtained from the theoretical and simulated methods. Construction of the selection index was complex in comparison to single trait selection, as each trait included in the index had to be assigned an economic value. This value is representative of the relative importance of that trait to the overall profitability, or ability to save costs in the operation. Therefore traits favourable to profitability, or having the ability to reduce production costs, are given a heavier weighting and will consequently achieve a relatively larger improvement when applied to the selection index. A model was constructed using production rates, income and costs to represent the current overall economic situation in the industry. This was then used to determine cost economic values, which represent the saving in cost per unit improvement in each of the economically important traits, and revenue economic values, calculated as the value of each unit improvement attained in each of the economically important traits. Body weight remains the most profitable trait in a broiler enterprise; however breeder egg production is equally important as the industry would fail without sufficient day-old broilers. Therefore, it would be beneficial to determine whether current egg production levels could be maintained, or even improved, whilst improvement is made to the growth rate of the progeny. The above statement was found to be possible with the use of index selection. This multiple trait selection strategy proved capable of defying the negative genetic correlation that exists between body weight and egg production by improving egg production to 60 weeks by eight eggs, and body weight at 35 days by 259 grams. Furthermore, in some cases index selection was able to achieve improvements in some traits greater than those attained with single trait selection, whilst simultaneously improving certain negatively correlated traits. Index selection has illustrated its superiority over single trait selection strategies and its relative value to the poultry industry.
Evaluating the efficacy of exogenous composite microbial enzymes in maize-soybean based broiler chicken feeds.
(2006) Ngxumeshe, Ayanda Mavis.; Gous, Robert Mervyn.
This research reported here was carried out to examine alternatives to antibiotic growth promoters as a result of their being banned in the animal feed industry. Four experiments were conducted to evaluate the efficacy of non-medicated feed additives as replacements for antibiotic growth promoters in broiler feeds. The additives used were enzymes (a new thermo-tolerant powder enzyme called TXAP, phytase, lipase and a new phytase enzyme derived from E. coli called phyzyme XP), organic acid (Acid Pak), prebiotic (Bio-Mos®) and probiotic (All-Lac XCL). Mashed maize-soya based feeds were used in all the experiments, which were conducted in litter-floor pens. The first experiment was a dose-response trial. Broilers in eight replicate pens of 50 males and 50 females were fed unsupplemented feeds and five additional feeds containing increasing levels of TXAP, from 0.5 to 2.5 g/kg to 42 d. The second experiment used enzyme TXAP with two different enzymes (phytase and lipase), individually or in combination. Six replicate pens of 50 males and 50 females were fed either unsupplemented feeds or one of six additional feeds treated with TXAP, lipase, phytase , a combination of TXAP and lipase, a combination of TXAP and phytase or a combination of all the three enzymes . This trial continued for 42 d. In the third experiment three types of TXAP (Lot 1, 2 and 3) were used, with fixed levels of xylanase and amylase but varying levels of protease activities (4000, 2000 and 1000 U/kg for Lot 1, 2 and 3, respectively) in combination with phyzyme XP for 35 d. The fourth experiment used mannan-oligosaccharide (Bio-Mos®), organic acid (Acid pak 2x), probiotic (All Lac XCL 5x), individually or in combination and an antibiotic growth promoter (Zinc bacitracin) for 42 d. The chickens in this experiment were challenged with Clostridium perfringens (CP) at 21, 22 and 23 d to determine the efficacy of these additives for replacing antibiotics in hindering the effects of CP on the villus surface area. The dose-response trial did not show any significant improvement in broiler performance with any level of inclusion of enzyme TXAP. The results from this study showed some beneficial effects with the use of enzyme TXAP when fed alone and at a young age. Its use when combined with other enzymes and at later stages of growth needs further investigation. Feed additives in experiment 4 prevented the negative effects of CP as the treated chickens did not have lesions on their villus surfaces. The conditions under which these trials were conducted appeared to be such that little benefit was derived from the use of any of the feed additives used. It is possible that under less-hygienic conditions such as those in commercial operations greater benefits from these additives may be realised.
An evaluation of effective energy in the formulation of diets for laying hens.
(1998) Young, Marion Belinda.; Gous, Robert Mervyn.
Emmans (1994) introduced a concept of energy utilisation applied across species, in which a heat increment in feeding is considered to be linearly related to five measurable quantities. Subtracting the heat increment of feeding from the metabolisable energy supplied defines the energy supply scale called effective energy. Two trial protocols were developed and run in controlled environment chambers at hot and cold temperatures using laying hens in individual cages. The first trial tested the response of hens at temperatures of 18°C and 32°C to the dilution of a basal diet with ingredients selected to promote a heat increment in different manners, according to the effective energy system. Diluents were soy protein isolate, fishmeal, sunflower oil, husks and sugar and starch mix. Six diets were offered to Amberlink and Hyline Brown hens for two successive periods of six weeks at the two temperatures. Responses in performance and calculated heat production indicated that heat increments could be induced by particular diluents. These affected the response in laying performance of the birds, particularly at high environmental temperatures. A second protocol tested the absolute value of the effective energy system by using Amber link hens for three consecutive seven week periods at 30°C, 20°C and 30°C, respectively. High and low effective energy diets were formulated, and blended, and compared against commercial high and low density diets. The effective energy diets and the commercial diets were also offered as a choice to the hens. The data illustrate a marked linear response to the effective energy in the diet. High effective energy produced the same response as a high nutrient density at high temperatures. Highest performances in lay were achieved on the choice diets. The hens demonstrated the ability to change the proportion of the choice of the effective energy diets at the different temperatures. Dynamic heat exchanges with the environment become significant, especially at higher temperatures in the thermally active hen. Effective energy considers this heat response, and can assist in ameliorating the response of the laying hen to high environmental temperatures when incorporated into principles of feed formulation.
Evaluation of techniques for improving broiler performance during the first week of life.
(2004) Mabusela, Thanduxolo Penrose.; Gous, Robert Mervyn.
The overall objective of this study was to evaluate the interventions that may be used to improve broiler performance during the first week of the life of a broiler chicken. Four experiments were conducted on caged broiler chickens. The interventions applied included the use of feeds varying in dietary protein contents, the use of pelleted vs. mash feed and the use of various feed additives, including additional vitamins and trace minerals, brewers yeast, Spirulina, conjugated linoleic acid (CLA) and an enzyme cocktail supplied by Optivite. In addition, access to feed was identified as a potential problem in the cages used in these trials, so feed trough position was tested, these being positioned either inside or outside the cages. The performance variables measured included growth rate, food intake and food conversion efficiency (FCE), the main objective being to maximise body weight at 7d. In all four experiments, broiler chickens showed a significant improvement in all variables when dietary protein content was increased, when pelleted feed was used, and when the feed was positioned inside the cage. No improvements occurred as a result of the addition of any of the feed additives except the enzyme cocktail from Optivite, which improved performance significantly. The best mean performance recorded over all the trials was on the highest protein feed (221g/kg) containing Optivite, when the feed was pelleted through a 1.8 mm die and fed inside the cage, the body weight of the chicks at 7d being 157 g, having consumed 164 g feed/chick at an FCE of 957 g/kg.
Factors influencing the rates of lipid deposition and withdrawal in growing pigs.
(2005) Sewjee, Rowena.; Gous, Robert Mervyn.
This study was conducted to determine the influence of factors on the efficiency of protein utilization and the rate of lipid deposition and withdrawal in growing pigs. Two experiments were conducted in total. The first experiment involved fifty-two crossbred entire Large White x Landrace male pigs, individually penned, which were used to test the proposition that the efficiency of protein utilisation is influenced by the body composition of the pig at the start of the trial. The experiment was divided into two phases: in the first period, starting at 20kg liveweight, when 3 pigs were slaughtered to determine the initial body composition of the pigs on the trial, the remaining 48 pigs were divided into three groups, two of which were fed ad libitum, with 11 pigs being offered a feed high in crude protein (HP, 1979 CP/kg) and 19 pigs being offered a low CP (LP, 166g/kg) feed. The remaining 19 pigs were fed HP on a restricted basis; the daily allowance being 0.7 of the mean intake of those pigs fed HP ad libitum. The objective of this initial period was to create three groups of pigs differing in body lipid content. As each pig achieved a protein weight of approximately 5.9kg, predicted to occur when the pigs on the three treatments reached live weights of 35, 39 and 34kg respectively, the pig entered phase 2 of the trial. At this stage three pigs from each treatment (a total of 9 pigs) were slaughtered for carcass analysis, the protein contents being approximately 5.9kg, and lipid contents being 85,98 and 87g/kg for the 3 treatments respectively. During phase 2, the 8 pigs fed HP in phase 1 continued to be fed HP in phase 2; 8 pigs were chosen at random from those fed LP in phase 1 and were allocated the high CP basal feed, while the remaining 8 were given LP; and 8 of the pigs feed-restricted in phase 1 were randomly chosen and fed HP, while the remaining 8 were given LP. All pigs were fed ad libitum during phase 2. Four pigs from each treatment in phase 2 were slaughtered after 1 week and the remaining 4 a week later for analysis of body composition In the first week of the second phase of the trial protein gain was highest (264g/d) on the pigs previously restricted and then fed HP, followed by those previously fed LP and then HP (242g/d), with pigs previously restricted and then fed LP depositing the least amount of protein (192g/d). Pigs fed LP or HP throughout, had protein gains of 217 and 210g/d, respectively. Efficiencies of utilization of dietary protein did not differ significantly between treatments, however, the highest being measured in pigs fed LP throughout (461g/kg), followed in order by those fed LP and then HP (457g/kg), those fed HP throughout (404g/kg), those previously restricted and then fed LP (394g/kg), with those previously restricted and then fed HP being the least efficient (372g/kg). The second experiment involved twenty-six male and twenty-six female crossbred Large White x Landrace pigs, individually penned, which were used to determine the maximum rate at which growing pigs can gain lipid. The experiment was divided into three phases: In the first, starting at 20kg live weight (56 days old), when two males and 2 females were slaughtered to determine the initial body composition of the pigs on the trial, the remaining 24 males and 24 females were randomly allocated to their various treatments. The treatments consisted of a feed high in crude protein (H, 197g/kg), a feed low in CP (L, 166g/kg) and three blends, namely 5OH/5OL (180g/kg) (male diet), 30H/70L (167g/kg) (both male and female diets) and 20H/80L (162g/kg) (female diet). Six pigs from each sex were allocated to each treatment. The EFG Pig Growth Model was used to determine the fat contents (lipid index) on the two feeds available and the three blends, to estimate the best times to sample pigs. It was estimated that phase 1 would terminate at 63 d, phase 2 at 70 d and phase 3 at 77 d of age. At the end of each phase two pigs from each sex and treatment were slaughtered. The lipid contents differed significantly between treatments at the end of phase 2 for the male pigs, with the highest being measured in pigs fed L (108g/kg), followed in order by those fed 70L/30H (86g/kg), those fed 5OL/5OH (74g/kg), and those fed H (68g/kg) with the least lipid content. The lipid contents of the female pigs were highly significantly different at the end of phase 3, with the highest being measured in pigs fed L (147g/kg), followed in order by those fed 80L/20H (124g/kg), those fed 70L/3OH (116g/kg) and the least lipid content from those fed H (115g/kg). As estimated by the EFG Pig Growth Model, the male and female pigs fed L treatment had the highest lipid content and those fed H treatment, achieving their target rate of lipid deposition, with the lowest lipid content. This study indicates that the response in protein gain and in efficiency of utilization of protein of pigs to a given feed is dependent on the amount and quality of the feed given to the animals previously. Also, the maximum rate of lipid deposition can be achieved by monitoring the changes in lipid deposition over a period of time, which enables an enhanced understanding of the theory of food intake regulation in a growing pig. As a result, accurate changes can be made when designing a phase-feeding program for growing pigs.
Improving calving rates in Afrikaner cattle.
(1997) Lishman, Arthur William.; Gous, Robert Mervyn.
No abstract available.