Abstract:
WOOL PRODUCTION OF SHEEP FED WEEKLY DIFFERENT AMOUNTS OF ROUGHAGES OF TWO PROTEIN CONCENTRATIONS P. McINNES* Summary The wool growth of groups of Merino, Polwarth and Corriedale sheep was measured when offered weekly roughages of different protein content. For five weeks, different amounts of each diet were offered so that one group of each breed gained body weight, the other lost weight. All groups were then offered for ten weeks amounts sufficient to maintain weight from the third to the tenth week. For each breed, when groups were offered more or less than energy requirements for maintenance, sheep fed the 18.3 per cent crude protein diet grew more wool than sheep fed the 8.0 per cent crude protein diet at a similar energy level. This difference was not observed in some groups until the following three weeks when maintenance energy levels were fed. For each breed, during the following seven weeks when weight remained relatively constant, there was generally no difference in the rate of wool growth between groups fed the different protein diets. The results indicate that similar nutritional parameters regulate wool growth of sheep maintaining weight, whether offered diets weekly or more frequently. I. INTRODUCTION Schinckel (1963) considered that when sheep are at maintenance or gaining weight, wool production is basically a function of 'the amount and composition of amino nitrogen at the absorptive level'. This suggestion is supported by the substantial increases in wool production in sheep which have received casein per abomasum (Reis and Schinckel 1961) or have been fed per OS casein previously treated with formaldehyde (Ferguson, Hemsley and Reis 1967). The amount of bacterial degradation of dietary protein and subsequent synthesis of bacterial protein in the rumen/reticulum is,-therefore, of utmost importance in obtaining a stimulus in wool production from dietary sources. Also the utilization of recycling endogenous nitrogen must be considered in circumstances when dietary protein content is low. The efficiency of utilization of dietary protein for wool production depends on the gain or loss of non-ammonia nitrogen (NAN) in the rumen/reticulum. There was little difference in the amount of NAN passing from the abomasum of sheep * Veterinary Research Station, N.S.W. Department of Agriculture, Glenfield, New South Wales. t Present address: Institute of Agriculture, University of Western Australia, Nedlands, Western Australia. 39 fed eight times daily the same amount of dry matter of two diets of different protein content (Hogan and Weston 1967a). Loss of nitrogen in the rumen/ reticulum of sheep fed the higher protein diet appear to be balanced by the utilization of nitrogen from endogenous sources in sheep fed the lower protein diet. Ferguson (1959) measured similar wool growth by sheep offered daily rations similar to those studied by Hogan and Weston (1967a), whose results, therefore, also support Schinckel's (1963) suggestion. Most experiments measuring responses in wool production to increases in dietary protein concentrations have been concerned with sheep offered mixtures of roughages and concentrates and fed daily at levels sufficient to maintain sheep at a constant bodv-weight. The nresent experiments were undertaken to measure the wool grown in sheep of thiee breeds fed weekly different energy levels of roughage diets of two protein concentrations. II. MATERIALS AND METHODS (a) Sheep Forty-eight Merino (Peppin), 28 Polwarth and 34 Corriedale wethers of about 23 years were used. Within each breed, sheep were divided into four groups by stratified sampling based on bodyweight. Some selection was then necessary so that for each breed group the mean greasy fleece weights, measured immediately before selection, were approximately the same. Two sheep of each group were used for studies on nitrogen balance and digestibility of the diets. The bodyweight of these sheep was near the mean of their respective group. (b) Diets Two roughages were fed:- chopped lucerne hay (roughage A), and a 3:l mixture of chopped oaten hay: chopped lucerne hay (roughage B). Roughages A and B contained respectively 18.3 per cent and 8.0 per cent crude protein (oven dry basis). (c) Experimental design and management Within each breed, two of the groups were offered for five weeks a high level of either roughage A or roughage B and, for the same period, the other two groups were offered a low level of either of the roughages (period 1). All groups were then offered for ten weeks the same roughage as fed in period 1 at a level which was calculated to maintain a group at a relatively constant mean body weight (period 2). In period 1, for all groups, the high feeding level provided similar amounts of digestible organic matter (DOM) per unit metabolic size, and similarly for groups fed the low level. Bodyweight changes of similar sheep at known DOM intakes were used as a guide in selecting feeding levels offered in period 2. Groups were fed weekly from self-feeders placed in open yards as described by Franklin (1952). Digestibility and nitrogen balance studies were made on sheep fed weekly and held in metabolism crates. Urine and faeces were collected daily for seven days as described by McInnes (1965). In period 1, these studies were made during week 4 for sheep offered the low feeding level, and during week 5 for sheep fed the high level. During period 2, the studies were made during weeks 9 and 10. 40 (d) Meizwrements Feed intake of the groups and bodyweights of all sheep weekly. Usually, sheep were fasted for 19 h before weighing, offered a high level of roughage during period 1, a fast of up to 50 at the end of the period in an attempt to equalise digesta fill in tract. Periodic wool growth was measured using the method of Wheeler (1963), the dye being applied via a hypodermic needle tached to a 10 ml syringe. (e) Chemical md statistical analysis were measured but for groups h was imposed the alimentary Chapman and (22 gauge) at- Dry matter, nitrogen and ash concentrations were determined by methods of A.C.A.C. (1955). Results were examined by analysis of variance. III. RESULTS Th,e mean bodyweights (*standard error of the mean) of the Merinos, Polwarths and Corriedales at the start of period 1 were respectively .35.7&O-8, 37.9& 1.2 and 44.9t 1.4 kg. Digestible organic matter intakes, nitrogen intakes, changes in mean bodyweights and clean fleece weights of the groups are given in Table 1. In all cases, bodyweights were corrected for wool growth. In both periods, the mean time taken to consume the weekly quantities was measured in sheep in metabolism crates. As there were no differences in the rate of intake between breeds, data from all breeds have pooled. During period 1, sheep consumed roughages A in 4.5 days at the high level of feeding, and in 3.0 days for the low level. In period 2, sheep consumed roughage A within 3.5 days. The corresponding values for sheep fed roughage B were 6.0 and 4.0 days for period 1, and 4.5 days for period 2. For both roughages, the rate of intake was more rapid for sheep offered the high level in period 1 than for sheep in period 2, which in turn was faster than when the low levels were offered in period 1 (P<O.O5). The nitrogen balances (not corrected for wool growth) were +40 g/wk and +36 g/wk for sheep fed the high levels of roughages A and B in period 1. The corresponding value for the low levels of feeding were + 13 g/wk and +3 g/wk. During period 2 for sheep offered roughages A and B, the nitrogen balances were +14 g/wk and +3 g/wk. IV. DISCUSSION Generally, wool production was unaffected by the protein concentrations of the roughage diets offered to sheep maintained at a relatively constant weight. However, there was a response in wool production to dietary protein when sheep were gaining or losing weight. The efficiency of utilization of dietary protein for wool growth in sheep fed weekly has not been studied, but values for nitrogen flow from the stomach of sheep offered similar diets daily, or more frequently, will be used in an attempt to explain the effect of dietary protein on wool production in this experiment. For all breeds, the ratio of dietary nitrogen to DOM (mg/g) of diet A and diet B for both periods was about 4.1 and 2.4 respectively. Using data of Hogan and Weston (1967b, 1968) for sheep fed eight times daily, the amount of NAN leaving the abomasum of sheep fed diet A and diet B would be about 75 per cent 41 TABLE 1 and 140 per cent of the dietary nitrogen. Thus, the daily mean NAN leaving the abomasum during the period when sheep were maintaining weight would be between 12 g (diet B) and 15 g (diet A). As there was, generally, no significant difference in wool production within breeds when sheep were maintaining weight in this experiment, it would appear on the basis of the results of Hogan and Weston (1967a) that similar amounts of NAN entered the small intestine. The calculations above indicate that there was little difference in the amount of NAN leaving the abomasum, and it would appear that similar nutritional parameters regulate wool production in sheep maintaining weight when fed weekly or more frequently. Wool growth of sheep gaining or losing weight was affected by the concentration of dietary protein, and this response occurred not only in some groups during period 1, but also as a delayed response (Reis and Schinckel 196 1; Sharkey and Hedding 1964) in some groups during period 2. Generally, during period 1 and/or during the first three weeks of period 2, sheep offered the high protein roughage grew more wool but reasons for these responses remain obscure. Using values of Hogan and Weston (1967b, 1968), at the higher levels of feeding, 23 g (diet A) and 20 g (diet B) NAN would have flowed from the stomach; at the lower levels of feeding, 11 g (diet A) and 10 g (diet B). Thus, greater wool growth of sheep fed the higher protein diet cannot be explained by NAN values deduced from measurements on sheep maintaining weight on diets fed more frequently. The increase in the rate of intake at higher levels of feeding could be associated with a more rapid passage of digesta through the rumen/reticulum (Balch and Campling 1962) and it is likely that a greater amount of dietary protein would be digested post-ruminally. This would favour higher wool production in sheep offered the higher protein diet. At the lower level of feeding in period 1, the interval of starvation between weekly feedings could have reduced the total bacterial activity so that less proteolysis and deamination occurred immediately after feeding commenced and, thus, again more dietary protein would be absorbed post-ruminally. A similar explanation could be given for sheep fed wheat weekly, which produced more wool than sheep fed daily (Hill, Watson and McClymont 1968). In the present experiment, however, there was little difference in the interval of starvation between sheep fed the low levels and when they were fed at maintenance during period 2. The inability to explain these results with a greater precision suggests that further investigation iso needed on the role of absorbed aminonitrogen in the regulation of wool production of sheep in conditions where nitrogen from tissue catabolism could supply nutrients for wool growth. There was little difference in the wool growth response between the three breeds. The efficiency of wool production (clean fleece weight/dry matter intake at maintenance) was in the ratio of 100:91:93 for the Merino:Polwarth:Corriedale. This relationship varies slightly from that of Daly and Carter (1955) who reported a ratio of 100: 106: 102 for the same breeds. In their experiment, finewool Merinos were used which have been shown by Dunlop, Dolling and Kennedy (1960) to be of lower efficiency than the Peppin strain used in this experiment. V. ACKNOWLEDGMENTS Thanks are due to Professor W. McManus and Dr. B. Setchell for their interests in these studies. VI. REFERENCES A.O.A.C. (1955). 'Official Methods of analysis of the Association of Official Agricultural chemists.' (Association of Official Agricultural Chemists: . Washington D.C.) BALCH, C. C., and C AMPLING , R. C. ( 1962). Nutr. Abstr. Rev. 32: 669. C HAPMAN , R. E., and W HEELER , J. L. (1963). Aust. J. Sci. 26: 53. D ALY , R. A., and C ARTER , H. B. ( 1955). Aust. J. agric. Res. 6: 476. D UNLOP , A. A., D OLLING , C. H. S., and K ENNEDY, J. F. ( 1960). Aust. J. agric. Res. 11: FERGUSON , FERGUSON, F RANKLIN , H ILL, M. 576. K A. (1959). Nature Land. 184: 907. K. A., H EMSLEY, J. A., and R EIS, P. J. ( 1967). Aust. J. Sci. 30: 2 15. K., W M. C. (1952). Aust. J. agric. Res. 3: 168. 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