The results of five experiments are reported as tests of a theory of the growth and feed intake of sheep. An attempt is first made to describe potential growth in the sheep, that is, growth under non-limiting conditions, and to generalise this description across breeds. The two ways of providing non-limiting conditions are then considered. This approach necessarily confronts the problem of predicting the desired intake of feed resources required to fulfill the potential. Whilst ad libitum access to a single,nutrient-rich feed is found an acceptable method, data collected in three experiments, using a total of 64 Suffolk X Greyface lambs, lead to theconclusion that sheep can also attain their potential for growth when given free and continual access to more than one feed, a possible combination of which is non-limiting to growth. It is suggested that the technique may be applied as an independent test of other estimates of resource requirements for growth and to the prediction of feeding behaviour in sheep. The responses of sheep to limiting conditions for growth are studied on the assumption that sheep have rules for partitioning the feed's first limiting resource. The limits to this view are investigated by experiment using 73 Scottish Blackface wethers offered amounts of feed which provide similar crude protein allowances but different yields of energy. It is concluded that the body composition of sheep can be manipulated by nutrition, since the animals will partition scarce energyresources to protein growth before fattening, but that this effect is complicatedin ruminants because protein supply is not independent of feeding level. The theory is then applied to the problem of predicting the recovery of sheep from the effects of growth restraint. An experiment involving 30 Scottish Blackface wethers provides data which support the idea that sheep, following a period of underfeeding, will resume their known potential for growth and, only when necessary, restore their body composition to the state dictated by their inheritance. No compensatory growth is observed. Finally, the work as a whole is discussed in relation to animal science and the sheepmeat industry. Possibilities for future research are also suggested. The experimental data are published in full in the appendices.

High-moisture barley, preserved either anaerobically, chemically or by drying, was evaluated in a series of digestibility and nitrogen utilization trials with monogastrics and ruminants. In the first of 3 phases, high-moisture barley HMB (17% moisture) from the Peace River region was preserved in experimental silos by: (1) airtight storage, (2) alkali - 3.2 g NaOH/kg HMB (air dry basis) in a 32% w/w solution, (3) acid - 1% mixture of 60:40 acetic-propionic acids and (4) drying - 8 tonnes per hour at 82°C. After 9 months of storage, these treatments were evaluated in a digestibility trial with pigs and a nitrogen balance trial with rats. In the pigs there was no treatment effect on dry matter digestibility, but neutral detergent fibre digestibility was reduced (P < 0.001) in the dried barley. True nitrogen digestibility, with both pigs and rats, was significantly (P < 0.001) reduced by alkali treatment. In the rat trial, alkali-treated barley depressed net protein utilization (NPU) by over 20%. Differences between the non-alkali treatments were small. Digestibility studies with sheep were not carried out on these treatments due to poor palatability results. In the second phase, barley from Lacombe was harvested at 33 and 12% moisture. The HMB (33% moisture) was either stored airtight or artificially dried (ADB) to 88% DM and the field-dried barley (FDB) (12% moisture) was either stored aerobically or reconstituted (RB) to 70% DM and stored airtight. These treatments were evaluated in a nitrogen balance trial with rats and a digestibility, nitrogen-retention trial with sheep. In the rat trial, true nitrogen digestibility was highest (P < 0.001) for HMB while biological valve was higher (P < 0.001) for both of the dry treatments. NPL) tended to be the same for all treatments. In the sheep trial, dry matter digestibility of RB was improved above ADB, but organic matter digestibility of both HMB and RB were greater than that of ADB (P < 0.01). Acid detergent fibre digestibility of HMB was highest (P < 0.001) followed by FDB and RB and then ADB. There was no treatment effect for either nitrogen digestibility or nitrogen retention. Straw from both HMB and FDB was also evaluated in sheep. Apparent dry matter, organic matter and nitrogen digestibility were all significantly (P < 0.001) greater for straw from HMB. The final phase of the study was conducted with barley of an unknown origin. Dry barley was reconstituted to 30% moisture (RB) and portions were treated with 3% NaOH (NaOH-RB) or 1% and 3% anhydrous ammonia (NH3-RB) on a w/w air dry basis. These treatments were again evaluated in a nitrogen balance trial with rats and a digestibility, nitrogen-retention trial with sheep. In the rat trial, true nitrogen digestibility for NaOH-RB was approximately 20% lower than the other treatments. Biological value and NPU were also depressed below all other treatments by NaOH-RB (P < 0.001). NPU for both 1 and 3% NH₃-RB were lower (P < 0.001) than RB after most of the NH₃ was allowed to evaporate for several days. However, there appeared to be no residual effect on protein utilization after the NH₃ was removed completely from the treated barley, as NPU for both 1 and 3% NH₃-RB were not different from RB. Dry matter digestibility was improved by all alkali-treatments (P < 0.001). In the sheep trial, both apparent dry matter digestibility and organic matter digestibility were significantly (P < 0.01) better for only the 3% NH₃-RB as compared to the other treatments. Acid detergent fibre digestibility was lower for 1 and 3% NH₃-RB than RB or NaOH-RB, between which treatments there were no significant differences. NaOH treatment reduced nitrogen digestibility by approximately 20 percentage units, but nitrogen-retention was unchanged between treatments with sheep. / Land and Food Systems, Faculty of / Graduate

High feed costs are part of any broiler rearing enterprise and continuous effort is required to help overcome this problem. The use of a feed expander may be beneficial in improving bird performance and thus increasing the profitability of broiler meat production. Four experiments were conducted to evaluate the performance of birds fed expanded feed in relation to the performance of birds fed non-expanded feed. The effect of feeding birds expanded feed was also tested under heat stress conditions. In this experiment, a significant improvement in cumulative feed conversion ratio (CFCR) was observed for birds fed expanded feed (Chapter 3). Pellet size influenced bird performance as birds fed a 3.2 mm non-expanded feed had a better cumulative FCR than the non-expanded 4.5 mm pellets, and this CFCR did not differ significantly from that in birds fed 3.2 mm expanded pellets (Chapter 4). There is, however, an improvement in the cumulative FCR to two weeks of age in birds fed expanded feed, over that in birds fed non-expanded feed, indicating that expanding of feed improves nutrient availability to the young broiler with a partially developed digestive tract. The effects of expanding feed on the body weight of birds were not consistent between experiments. This might be attributed to expanding temperature, as the feed in Chapters 3 and 4 was expanded at 90°C and not at higher temperatures as in the other chapters. Expanding feed at 90°C may not allow proper starch gelatinisation and alteration of nutrient availability. Expanded feed had better pellet durability than non-expanded feed and there were no significant negative effects on vitamin recovery, enzyme stability and nutrients when feed was expanded at temperatures between 95 and 1 05°C. Pellet quality increased with an increase in expanding temperature. Expanding of broiler feed led to a significant improvement in lipid digestibility (Chapter 6). Expanding of feed at 105°C is recommended as feed expanded at this temperatures tend to have significantly higher AMEn values for broilers than non-expanded feed. / Dissertation (MSc(Agric))--University of Pretoria, 2012. / Animal and Wildlife Sciences / unrestricted

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Feed represents a large portion of input costs for dairy operations. Decreasing the feed consumed, measured here as dry matter intake (DMI), would therefore be advantageous to producers. However, this decrease could result in cows that do not supply the necessary energy to maintain high production, growth, and reproduction. Measures of feed efficiency try to capture important energy expenditures to ensure that cows consume less while maintaining production. Feed efficiency in this study is measured in residual feed intake (RFI), which is calculated as the difference between DMI and expected DMI based on production and growth measures. However, the RFI model does not capture the energy stores required for reproduction; therefore, selection for RFI may lead to reduced reproductive performance. In this thesis, I explored the phenotypic and genetic relationships between RFI, DMI, and reproductive performance as measured by number of services (NS), days open (DO), and days to first calving (DFC). First, ANOVA tests and phenotypic correlations determined the phenotypic relationship between the traits. Then, heritability and genetic correlations were used to estimate the genetic parameters. Phenotypically, results indicated mixed relationships between traits. Heritability estimates were low for reproductive traits and moderate for DMI and RFI. There was no unfavorable genetic relationship between DMI or RFI with any of the reproductive traits. Therefore, neither selection for DMI nor RFI will unfavorably impact reproduction. / Master of Science / Dairy cows consume significant resources in the form of feed. Decreasing the feed consumed, measured here as dry matter intake (DMI), would therefore be advantageous to producers and consumers. However, this decrease could result in cows that do not supply the necessary energy to maintain high production, growth, and reproduction. Measures of feed efficiency try to capture important energy expenditures to ensure that cows consume less while maintaining production. Feed efficiency in this study is measured in residual feed intake (RFI), which is calculated as the difference between DMI and expected DMI based on production and growth measures. However, the RFI model does not capture the energy stores required for reproduction; therefore, selection for RFI may lead to reduced reproductive performance. In this thesis, I explored the phenotypic and genetic relationships between RFI, DMI, and reproductive performance as measured by number of services, days open, and days to first calving. First, ANOVA tests and phenotypic correlations determined the phenotypic relationship between the traits. Then, heritability and genetic correlations were used to estimate the genetic relationship between traits. Heritability estimates were low for reproductive traits and moderate for DMI and RFI. There was no unfavorable genetic relationship between DMI or RFI with any of the reproductive traits. Therefore, neither selection for DMI nor RFI will unfavorably impact reproduction.