Responses to dietary protein supplements

H . Galbraith Livestock Production Science 64 2000 81 –93 83 1.2. Characteristics of caprine hair fibre and 20 or greater in the high sulphur cysteine-rich amino acid composition of hair , body tissues and fraction of the matrix proteins. protein supplements Overall concentrations of cysteine including that present in its dimer form cystine for mohair and The major goat fibre products are mohair produced sheep wool in comparison with muscle and sources by the essentially single-coated genetically-distinct of dietary supply are shown in Table 1. The main Angora goat and cashmere which is produced by the points to note are the greater concentrations of more genetically heterogeneous double-coated Cas- cysteine in mohair and wool than muscle, rumen hmere goat. Both fibre types are produced by sec- microbial protein and the examples of dietary protein ondary hair follicles. Mohair fibres are lustrous, non- supplements, soya bean meal and white fishmeal medullated, grow at up to 2.5 cm month and range Galbraith, 1998. The supply of sulphur amino acids in diameter from 22 to 45 mm, with annual greasy above that supplied by microbial protein also de- fleece yields of up to 6 kg. Cashmere, which is the pends on the digestibility of the rumen-undegraded fine undercoat, grows at up to 1.5 cm month, fraction of the dietary supplement. although frequently less, with commercially accept- able diameter in the range of 12–18 mm, and yields of 50–600 g year. Growth of cashmere, unlike

2. Responses to dietary protein supplements

mohair, is dependent on photoperiod. Guard hair, the coarse overcoat of the Cashmere goat is produced by 2.1. Response of Angora goats to variations in primary follicles and also grows seasonally with dietary protein and energy diameters in the range 30–90 mm with length 4–20 cm and yields up to 500 g year. The commercial The effect of two levels of dietary protein and value of cashmere and Angora fibre products is energy see Table 2 was studied for 112 days in 24 optimised by high yields, small diameters and ab- Australasian-type yearling castrate male Angora sence of primary fibres and other contaminants. goats weighing | 22 kg Shahjalal et al., 1992. Hair is produced by follicles situated in the skin of Protein supplementation was provided by a mixture animals. The hair product is composed largely of of equal quantities of white fish meal and soya bean cells of the cortex which contain large amounts of meal to give estimated concentrations g kg dry intermediate filament proteins IFPs including matter, DM for rumen undegradable protein UDP keratins and a non-filamentous matrix containing of 26 LP and 79 HP and for rumen degradable intermediate filament-associated proteins IFAPs. protein RDP 82 LP and 101 HP, respectively. The IFPs are considered to contain concentrations of Positive responses in mid-side raw fibre yield, to the the sulphur amino acid cysteine residues per 100 increase in dietary crude protein concentration from residues of amino acids of approximately 6.0 with 108 to 180 g kg DM, occurred in the first 4 weeks Table 1 Relative composition of selected amino acids, g amino acid 16 g N in tissues and dietary protein sources modified from Souri et al., 1997 and Galbraith, 1995 Amino Mohair Wool Muscle Rumen Extracted White acid microbial soyabean fishmeal protein meal Threonine 5.9 5.5 3.9 5.2 4.2 4.2 Leucine 8.6 6.5 5.8 7.4 8.2 6.7 Phenylalanine 3.6 4.6 3.1 5.5 5.5 3.9 Lysine 2.9 3.5 5.9 8.1 6.8 5.7 Methionine 0.4 0.6 1.8 2.5 1.4 3.0 Cysteine 12.5 9.1 1.1 1.0 1.4 0.9 84 H . Galbraith Livestock Production Science 64 2000 81 –93 Table 2 Raw yield and diameter of mid-side mohair fibre of Angora goats given diets containing per kg DM 10.0 MJ LE or 11.9 MJ HE and 108 g LP or 180 g HP crude protein modified from Shahjalal et al., 1992 a Raw fibre yield Treatments Significance of contrast 2 g 100 cm LE–LP LE–HP HE–LP HE–HP SED P E Period of treatment weeks 1–4 1.68 2.49 1.65 2.11 0.357 NS 5–8 2.88 3.97 3.05 3.53 0.335 NS 9–12 2.50 3.74 3.19 3.75 0.319 NS 13–16 1.74 3.14 2.59 3.31 0.279 1–16 8.91 13.3 10.5 12.7 1.08 NS Fibre diameter mm 29.9 35.6 32.4 35.8 1.49 NS day 112 a P, protein; E, energy no significant interaction effects were recorded; P , 0.05, P , 0.01, P , 0.001. and were maintained throughout. There was no follicles for supplementary nutrients are shown in significant response to energy until the final 3 weeks. Table 3. On average, the higher supply of dietary These data confirm earlier reports e.g. Shelton and energy increased live weight gain LWG, efficiency Huston, 1966; Deaville and Galbraith, 1992; Sahlu et of food conversion, empty digesta-free body weight al., 1992; Reis and Sahlu, 1994 which suggested and weights of chilled carcass and dry matter, crude that growth of mohair may be limited by inadequate protein, lipid and ash in bone-free dissected carcass supply of protein in the diet and that protein supple- tissue. All of these parameters were improved by the mentation stimulated yield but produced commercial- dietary protein supplementation. In addition, the ly undesirable increases in fibre diameter. presence of statistically significant interactions be- The effect of variations in dietary protein and tween dietary protein and energy suggested that energy on growth and carcass and body components responses to a protein supplementation were great- which would be expected to compete with hair est on the low energy diet and to b energy Table 3 Growth performance and selected carcass characteristics of Angora goats given diets containing per kg DM 10.2 MJ LE or 11.9 MJ HE and 108 LP or 180 g HP crude protein modified from Shahjalal et al., 1992 a Treatments Significance of contrasts LE–LP LE–HP HE–LP HE–HP SED P E I Live-weight gain 48 80 91 116 7.26 LWG, g day Food conversion efficiency 0.062 0.099 0.117 0.139 0.0078 LWG DMI Empty body weight 23.5 28.5 29.0 31.3 0.821 EBW, kg Gut contents kg 3.83 4.16 2.99 3.71 0.344 Chilled carcass weight 12.1 15.3 15.2 16.8 0.507 CCW, kg Weight of carcass kg Dry matter 2.16 2.89 3.06 3.32 0.163 Crude protein 0.697 0.867 0.877 0.967 0.051 Lipid 1.18 1.82 2.00 2.13 0.130 Ash 0.035 0.045 0.044 0.049 0.0032 a P, protein; E, energy; I, interaction. P , 0.05, P , 0.01, P , 0.001. H . Galbraith Livestock Production Science 64 2000 81 –93 85 supplementation were greatest on the low protein 82.3, respectively. The data were examined by diet. These results contrast with these for hair growth analysis of variance and the significance of linear L Table 2 where consistent responses were obtained quadratic Q and cubic not shown relationships only for dietary protein supplementation and where between treatments determined. There were no ef- statistically significant interactions were not ob- fects of dietary treatment on the intakes of dry matter tained. The results are also seen to contrast with or estimated metabolisable energy. As planned, those reported by Sahlu et al. 1992 in which intakes of crude protein increased linearly according 21 increases in crude protein, up to 190 g kg in to concentration present in each diet. isoenergetic diets resulted in greater yields of both The clean fibre yield was significantly affected Q; raw and clean fibre, but had no effect on body P , 0.05 between day 1 and 56 with increases up to 21 weight gain of 18-month-old female Angora goats. 165 g kg DM and a decrease at the highest 21 The reasons for the differences in response are not concentration of 185 g kg DM. Fibre diameter clear, but may relate to differences in sex i.e. increased linearly L; P , 0.05 as the protein intake castrate males versus females and the potential for was raised. The data indicate that a concentration of 21 growth. 165 g kg DM may be most appropriate for optimising fibre yield, but not diameter, the lowest 2.2. Optimisation of dietary protein concentration value for which was recorded on the diet providing for mohair fibre production least dietary crude protein in the present study. In view of the apparently positive relationships between The question of optimising dietary protein con- fibre yield and diameter, decisions on the most centration to balance benefits in fibre yield against economic concentrations of dietary protein will increases in diameter such as these demonstrated in depend on the balance between the relative values of Table 2 was investigated in a further study Shahjalal the weight and fineness of fibre produced where et al., 1991 Table 4. In this 63-day study, 20 control of protein nutrition can be achieved. Similar Australasian type male castrate Angora goats, aged studies designed to determine the requirements for about 16 months and weighing 28 kg on average dietary nutrients for cashmere goats have been were offered diets containing an estimated 9.6 MJ conducted under Australian conditions by, for exam- 21 kg DM metabolisable energy at intakes of 55 g ple, Ash and Norton, 1987a,b; McGregor, 1988 and 0.75 DM kg LW with variations in crude protein CP Kloren et al., 1993a,b. Variables measured included achieved by replacing dietary sugar beet pulp with a effects of dietary protein and energy in addition to mixture of soya bean meal and fish meal. Estimated age and sex of goat, pregnancy, lactation and dy- dietary rumen degradable and undegradable protein namic changes in photoperiod. Of particular impor- 21 g kg DM ranged from 74.5 to 103 and 27.5 to tance is the description of responses to protein Table 4 Mid-side clean fibre yields, intakes of dietary dry matter, crude protein and estimated metabolizable energy, and fibre diameter of Angora goats given diets differing in crude protein concentration modified from Shahjalal et al., 1991 a Treatment means Statistical b Dietary crude protein g kg DM significance 102 126 165 185 SED L Q Dry matter intake kg 44.1 38.2 42.9 41.0 2.30 NS NS Crude protein intake kg 4.16 4.84 7.08 7.57 0.33 NS Est. ME intake MJ 395 364 410 410 22.2 NS NS 2 Clean fibre yield g 100 cm 3.43 3.99 4.89 3.20 0.547 NS day 1–56 Fibre diameter mm day 56 29.8 31.5 36.1 33.6 1.77 NS a Data have been adjusted for initial fibre yield day 0 as covariate. b See text P , 0.05. 86 H . Galbraith Livestock Production Science 64 2000 81 –93 supplementation only under conditions of sub- usually not limited by protein nutrition. There is, in maintenance levels of nutrition e.g. McGregor, contrast, evidence for increases in guard hair pro- 1988. duction following improved dietary nutrient supply see Russel, 1995. 2.3. Effect of nitrogen source on cashmere production 2.4. Effect of protein nutrition on cellular characteristics of wool hair follicles Cashmere is an economically more valuable fibre than mohair and there is considerable interest in Hair follicles arise as a result of the proliferation means of improving yield. The effect of protein of cortical and associated cells of the follicle bulb nutrition was therefore studied in 24 male castrate and cortical cell differentiation to form the hair shaft. Cashmere goats 12 Siberian S 3 Irish feral and 12 These processes have not yet been quantitatively Australian A 3 Irish feral in a 102-day study described for caprine hair follicles. However, some Galbraith et al., 1994. Within genotypes the goats indication of cellular events may be obtained from were allocated to receive nitrogen supplementation the study of Hynd 1989 which investigated protein either based on urea 1 sodium sulphate U or white supplementation of sheep which are considered to fish meal F to give estimated concentrations respond similarly to Angora goats Russel, 1995. In 21 g kg DM of RDP and UDP of 86 and 64 and this study the effect of alterations in protein nutrition 117 and 32 for diets F and U, respectively, with an on wool follicle cell kinetics was determined using 21 estimated ME concentration of 11.0 MJ kg DM Merino and Corriedale breeds. The sheep, aged 3 for the basal diet. Mid-side total fleece growth years, were offered diets containing 15 g N and 9.1 measurements indicated no significant effects due to MJ metabolisable energy ME per kg DM at a protein supplementation Table 5, selected data maintenance level for 9 weeks, followed by an 8- shown with no significant alteration in the pro- week period of supra-maintenance feeding of a diet portions by weight of guard hair to cashmere. There containing an estimated 51 g N and 10 MJ ME per were similarly no effects of source of protein supple- kg DM and designed to provide 6 g per day of ment on the average diameter of cashmere fibres. cystine for post-ruminal absorption. Measurements These results confirm others in the literature as of clean wool growth were made over the last 3 reviewed, for example, by Restall et al. 1994, weeks and other fibre and hair follicle characteristics Russel 1995 and Souri et al. 1998a that a under were studied for the final 7 days of each feeding these or similar conditions, and above maintenance period. Selected results are shown in Table 6. The levels of nutrition and b unlike mohair production change from the low protein to the higher protein by Angora goats see Table 2, cashmere growth is diet resulted in a significant increase in the rate of Table 5 Nutrient intake, mid-side fleece growth cashmere 1 guard hair, day 49–97, proportion of cashmere and guard hair and fibre diameter of Siberian S and Australian A cross Irish feral goats given dietary supplements of urea U or white fishmeal F modified from Galbraith et al., 1994 Treatments SU SF AU AF SED Dry matter intake kg 74.2 76.4 76.3 74.9 10.4 Crude protein intake kg 11.1 11.5 11.4 11.2 1.53 Est. ME intake MJ 767 798 782 787 105 2 Mid-side growth g 100 cm 0.93 1.26 1.31 1.19 0.58 Day 97 Guard hair 0.65 0.73 0.87 0.77 0.14 Cashmere 0.35 0.27 0.13 0.23 0.14 Cashmere fibre diameter mm 17.4 17.7 16.5 17.4 0.58 H . Galbraith Livestock Production Science 64 2000 81 –93 87 Table 6 Mean values with S.D. for fleece, fibre, wool follicle and cellular characteristics of sheep offered diets containing either 15 low or 51 high g N kg DM see text for details: modified from Hynd, 1989 N in Fleece Fibre Fibre Cortex Total no. No. of No. of diet growth diameter length volume of bulb mitoses cortex cells 21 23 3 21 21 21 g N kg g day mm mm day 10 3 mm h cells h produced h 15 10.5 25.3 378 7.4 909 26 8.0 S.D. 1.8 2.5 30 1.7 221 4.7 1.4 51 14.0 27.2 475 11.0 1177 35 11.3 S.D. 2.9 3.5 44 3.2 309 7.0 2.8 wool production associated with increases in the periods, whereas responses to cashmere were ob- germinative volume of the bulb, rates of fibre tained from days 31–58 only. These responses of elongation and proliferation of cells of the bulb. This increasing yield without affecting diameter indicate latter response is of particular interest since it implies greater growth due to an enhanced rate of elongation a direct local effect of nutrition supply on the for the cashmere fibre. Guard hair was not affected mechanisms responsible for cell division, including by supplementation. The presence of significant those at the level of the gene and or an indirect interactions indicates the generally greater response effect involving stimuli perhaps of systemic hormon- of Angora goats to supplementation. However, the al or more local paracrine origin. It may be con- positive response for cashmere production contrasts cluded from these results that the effects of improved with the report by Ash and Norton 1987a who protein nutrients are more complex than those pro- observed no response in cashmere growth to dietary duced solely as a consequence of improved amino supplements of methionine in 3–4-year-old Aus- acid supply for protein synthesis in the proliferating tralian Cashmere entire males live weights were not and differentiating cortical cells which form the hair reported and when differences in total hair growth fibre. were attributed to an increased production of guard hair by primary follicles. This latter result for cashmere is consistent with the absence of response

3. Responses to rumen-protected methionine to improved protein supply at supra-maintenance