Effects of dietary protein sources on mohair growth and body
weight of yearling Angora doelings
A.J. Litherland, T. Sahlu
*, C.A. Toerien, R. Puchala, K. Tesfai, A.L. Goetsch
E (Kika) de la Garza Institute for Goat Research, Langston University, Langston, OK 73050, USAReceived 25 April 1999; accepted 1 February 2000
Abstract
Fifty-one yearling Angora doelings (200.6 kg initial body weight (BW)) were used to determine effects of different dietary protein sources on BW change and mohair growth. Diets consisted of approximately 40% roughage and 18±19% CP (DM basis), of which two-thirds was supplied by corn gluten meal (CG), cottonseed meal (CT), hydrolyzed feather meal (FT) or menhaden ®sh meal (FI); DM intake was restricted at approximately 0.7 kg/day. During the 94-day experiment, ¯eece-free ADG was greatest (P<0.05) for FI (35, 33, 35 and 50 g), whereas greasy ¯eece weight was greatest (P<0.05) for CG (4.4, 3.6, 3.4 and 3.4 kg for CG, CT, FT and FI, respectively). Likewise, mohair growth rate was greatest among treatments (P<0.05) for CG in each of the three 31- or 32-day periods. Ruminal ¯uid ammonia N concentration was 8, 11, 6 and 13 mg/dl (S.E. 1) immediately before feeding; 10, 18, 11 and 23 mg/dl (S.E. 2) at 2 h after feeding; 8, 15, 10 and 18 mg/dl (S.E. 2) at 4 h after feeding; and 4, 6, 5 and 8 mg/dl (S.E. 1) at 6 h after feeding for CG, CT, FT and FI, respectively. Total VFA concentration in ruminal ¯uid was similar among treatments (P>0.05) at 4 and 6 h, but was generally lower for CG and FT than for CT and FI immediately before feeding (29, 33, 26 and 37 mM; S.E. 2) and at 2 h after feeding (44, 57, 45 and 51 mM for CG, CT, FT and FI, respectively; S.E. 3). In conclusion, the different protein supplements had dissimilar effects on ADG (greatest for FI) and mohair growth (greatest for CG). Factors responsible for these results are unclear, and the range of experimental or production conditions under which comparable ®ndings might occur are unknown and deserve further study.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Angora goats; Mohair; Protein supplements
1. Introduction
Angora goat farming in the US occurs in areas such as Texas, where cottonseed meal is the supplemental protein source of choice, but also in regions where other protein sources are available and relatively inexpensive. In comparison with cottonseed meal, protein sources such as hydrolyzed feather meal, corn
gluten meal and ®sh meal are more resistant to ruminal degradation and contain high concentrations of sulfur amino acids.
The US Angora goat, on a body weight (BW) basis, is one of the highest ¯eece-producing ruminants (Litherland and Sahlu, 1997). Mohair growth requires little energy but much protein is needed. In particular, requirements for the sulfur-containing amino acids cysteine and methionine are high (Reis and Sahlu, 1994). Based on amino acid concentrations, ruminal microbial protein cannot supply suf®cient sulfur amino acids for mohair growth (Qi et al., 1994).
*Corresponding author. Tel.:1-405-466-3836;
fax:1-405-466-3138.
E-mail address: sahlu@mail.luresext.edu (T. Sahlu)
Feeding protein sources with high concentrations of sulfur amino acids, which are generally resistant to ruminal degradation, can alter postruminal amino acid supply (Cecava et al., 1990). When additional sulfur amino acids have been supplied postruminally to the Angora goat, mohair growth increases (Sahlu and Fernandez, 1992). However, the array of amino acids needed for ¯eece-free BW gain is different from that needed for ®ber growth. Thus, diets containing sup-plemental protein sources promoting high BW gain may not necessarily do so for ®ber growth, which would be of special importance for growting, ®ber-producing ruminants, such as yearling Angora doel-ings typically bred for kidding at 2 years of age. Therefore, objectives of this study were to determine if different common supplemental dietary protein sources have similar effects on live weight and mohair growth in yearling Angora doelings.
2. Materials and methods
2.1. Animals and experiment design
Fifty-one 1-year-old Angora doelings, averaging 20 kg BW (S.E. 0.6), 3.0 kg ¯eece weight (S.E.
0.18; shorn on 22 February) and 26.6mm ®ber dia-meter (S.E. 0.29), were used in the experiment. For allocation to treatments, ®rst animals were ranked or strati®ed by BW, then randomly allocated within BW grouping to the four treatments. After this initial allocation, means and S.D. for each treatment were calculated for BW, ¯eece weight and ®ber diameter. Some changes in treatment allocation were made to achieve similar means and variation within treatments for these variables. There were three treatments with 13 animals and one with 12. Once the four treatment groups had been formed, they were randomly assigned to the dietary treatments. Dietary treatments were different supplemental protein sources: cottonseed meal (CT; 41% CP, DM basis), corn gluten meal (CG; 73% CP, DM basis), hydrolyzed feather meal (FT; 90% CP, DM basis) and Menhaden ®sh meal (FI; 66% CP, DM basis). The protein sources composed between 10 and 24% of dietary DM and supplied 65±70% of total dietary CP (Table 1). Diets were formulated to be 65% total digestible nutrients and 18% CP (DM basis). The experiment commenced on 28 March and was 94 days in length. Doelings were housed individually, subjected to ambient temperature and natural photo-period and had ad libitum access to water. Feed was offered once daily at a constant level, which was
Table 1
Diet composition (% dry matter)
Item Dieta
CG CT FT FI
Ingredient composition
Cottonseed hulls 43.20 36.90 40.80 40.60
Ground corn 41.00 37.20 47.10 43.50
Corn gluten meal 14.00
Cottonseed meal 23.80
Feather meal 10.10
Fish meal 14.50
Calcium carbonate 0.65 0.90 0.80 0.25
Trace mineral premixb 1.00 1.00 1.00 1.00
Vitamin premixc 0.20 0.20 0.20 0.20
Chemical composition
Crude protein 18.2 18.9 19.4 18.6
Neutral detergent fiber 49 44 48 46
Acid detergent fiber 31 24 28 31
Ash 4 6 6 5
aCG: corn gluten meal; CT: cottonseed meal; FT: hydrolyzed feather meal; FI: ®sh meal.
calculated based on individual BW and assuming 0.119 M cal ME/kg0.75 BW required for BW main-tenance and mohair growth and an additional 0.007 M cal ME/kg ADG for 100 g ADG (NRC, 1981), since at approximately 1 year of age the doel-ings still had growth potential and would need to increase in BW for kidding at 2 years of age.
2.2. Measures
Doelings were weighed before feeding at 2 weeks intervals. Every 31 or 32 days, ®ber regrowth rate and ®ber diameter were estimated by clipping a 12 cm 12 cm square on the right mid-side. At the end of the experiment, doelings were shorn, ¯eece weight was measured and a grab sample was removed from the left mid-side for determination of ®ber diameter, stretched staple length and kemp. Greasy and clean mohair weights were determined according to ASTM (1988). Fiber diameter, percentage of kemp ®bers and diameter of kemp ®bers (patch samples) were deter-mined on 3000±4000 snippets using an optical ®ber distribution analyzer (OFDA 100; Zellweger Uster, Inc., Charlotte, NC, USA). Feed ef®ciencies were calculated for ¯eece-free BW and ¯eece mass.
On Days 45 and 90 of the experiment, ruminal ¯uid was sampled at 0, 2, 4 and 6 h after feeding. Con-centrations of amino acids in protein supplements were determined as described by Puchala et al. (1995) using an AminoQuant system (Hewlett Packard, San Fernando, CA) and precolumn derivatization witho -phthalaldehyde and 9-¯uorenylmethyl-chloroformate and UV detection. Ruminal ¯uid was sampled by stomach tube, acidi®ed with HCl, frozen at ÿ208C and later assayed for ammonia N by the phenol-hypochlorite procedure of Broderick and Kang (1980) and VFA by gas chromatography (Hewlett Packard, Avondale, PA) as described by Lu et al. (1990). Daily samples of diets and feed refusals were used to form composites for three 31- or 32-day periods. Composite samples were ground to pass a 1 mm screen and analyzed for ash, CP (AOAC, 1984), NDF and ADF (Goering and Van Soest, 1970).
2.3. In situ N disappearance
Three mature, ruminally cannulated Angora wethers were fed a diet composed of equal parts of
the four diets with different protein sources at 120% of the ME requirement for BW maintenance. After a 2 weeks adaptation period, duplicate dacron bags (14 cm9 cm bags; 50mm pore size) containing 3.1 g (DM) of the protein sources (ground to pass a 2 mm screen) were incubated in the rumen for 2, 4, 8, 12, 24 or 48 h. Bags were emersed in tap water before incubation. Also, loss through solubilization and washout through bag pores (i.e. 0 h disappearance) was estimated by soaking in water for 20 min. After removal of bags from the rumen, bags were immedi-ately emersed in cold water then washed in cold water in a washing machine for 10 min, dried for 24 h at 558C and analyzed for N. Extent of ruminal N dis-appearance was calculated as described by érskov (1990) assuming a ruminal digesta passage rate of 0.05/h.
2.4. Statistical analyses
Single time-point measures were analyzed with treatment in the model by general linear models procedures of SAS (1990), and differences among means were determined by least signi®cant difference and a protected F-test (P<0.05). Patch sample mea-sures, including clean mohair growth rate, were ana-lyzed separately for each 31- or 32-day period. Ruminal ¯uid measures with different days and times of sampling were analyzed by repeated measures analysis and the Wilks' Lambda test of signi®cance.
3. Results
3.1. Diet composition
The dietary CP concentration was similar to that formulated for (Table 1), and NDF concentration did not differ greatly among treatments. The extent of in situ ruminal N disappearance was 38, 61, 33 and 51% for corn gluten, cottonseed, feather and ®sh meals, respectively.
3.2. ADG and ¯eece
(P>0.10; Table 2). Fleece-free ADG was greatest (P<0.05) among treatments for FI, whereas greasy ¯eece weight was greatest (P<0.05) for CG. In part because of greatest ADG and grease ¯eece weight for FI and CG, respectively, ®nal BW was similar among treatments (P>0.10). Treatment differences in ratios of ¯eece-free ADG and grease ¯eece weight to DM intake were similar to those in ADG and grease ¯eece weight. Fiber diameter, stretched staple length and percentage of kemp ®ber were similar among treat-ments (P>0.10).
Clean ®ber yield averaged 81% of grease ¯eece weight. In agreement with greatest grease ¯eece weight for CG, clean mohair growth rate was greatest
(P<0.05) among treatments for CG (Table 2). In general, the magnitude of difference was similar among 31- or 32-day periods. Other period measures (®ber diameter, percentage kemp and kemp ®ber diameter) were not affected by treatment (P>0.10).
3.3. Ruminal ¯uid ammonia N and VFA concentrations
Day effects and interactions were nonsigni®cant (P>0.05) for ruminal ¯uid ammonia N and VFA concentrations. Interactions between time after feed-ing were signi®cant (P<0.05) for ruminal ¯uid con-centrations of ammonia N and total VFA, but not for Table 2
Effects of dietary protein source on dry matter intake, average daily gain and ¯eece measures in yearling Angora doelingsa
Item Dietb S.E.
CG CT FT FI
DM intake (kg/day) 0.71 0.69 0.72 0.71 0.02
Final body weight (with fleece; kg) 25 24 24 26 1
Fleece-free ADG (g) 35 b 33 b 35 b 50 a 4
Greasy fleece weight (kg) 4.4 a 3.6 b 3.4 b 3.4 b 0.1
Fleece-free ADG:DM intake 49 b 47 b 50 b 69 a 5
Greasy fleece weight:DM intake 44 a 35 b 34 b 34 b 2
Day 94 whole fleece measures
Fiber diameter (mm) 31.6 29.9 29.9 29.6 0.7
Stretched staple length (cm) 10.2 10.1 9.0 9.1 0.4
Kemp (%) 0.28 0.14 0.18 0.20 0.03
Patch sample measures
Clean mohair growth rate (mg cmÿ2per day)
Day 1±31 1.46 a 1.23 b 1.23 b 1.25 b 0.06
Day 32±62 1.66 a 1.39 b 1.27 b 1.35 b 0.08
Day 63±94 1.55 a 1.32 b 1.26 b 1.27 b 0.08
Fiber diamter (mm)
Day 1±31 30.4 29.0 29.6 29.0 0.6
Day 32±62 31.8 30.1 30.4 30.4 0.7
Day 63±94 33.7 31.9 31.8 31.7 0.7
Kemp (%)
Day 1±31 0.20 0.18 0.22 0.21 0.04
Day 32±62 0.32 0.22 0.29 0.28 0.05
Day 63±94 0.46 0.18 0.29 0.30 0.05
Kemp fiber diameter (mm)
Day 1±31 59 60 57 59 3
Day 32±62 63 61 59 62 3
Day 63±94 74 66 65 64 5
aWithin a row, means without a common letters differ (P<0.05).
molar VFA percentages. In general, ruminal ammonia N concentration was greater for CT and FI than for CG and FT, with differences at 6 h of lesser magnitude than at other times (Table 3). In general, differences among treatments and trends for differences in total VFA concentration were similar to those in ammonia N concentration. Molar percentages of acetate and propionate and the acetate to propionate ratio were similar among treatments (P>0.05). The butyrate molar percentage was greatest among treatments for CG (P<0.05).
4. Discussion
4.1. Ruminal protein disappearance and nitrogenous compounds
Extents of ruminal disappearance of supplement protein estimated in situ were within ranges reported for other ruminant species of 15±55% for CG, 30±70% for FI, 29±40% for FT and 46±68% for CT (NRC,
1985; Titgemeyer et al., 1989; Calsamiglia et al., 1995; Yoon et al., 1996; Piepenbrink and Schingoethe, 1997). Values for FI, FT and CT fell within four percentage units of mean values presented by NRC (1985), although the estimate for CG was seven percentage units less than that given by NRC (1985). The in situ ruminal protein disappearance estimates agree with differences among diets in rum-inal ammonia N concentration.
Ruminal ammonia N concentrations were low con-sidering the relatively high dietary CP level, which can be at least partially explained by the high level of dietary inclusion of the protein sources, some of which were low in ruminal degradability, and moderate to high level of ground corn. Ruminal ammonia N con-centrations at 6 h post-feeding were near the level of 2±5 mg/dl, often considered required for normal microbial growth (Satter and Slyter, 1974). Therefore, at later times after feeding ruminal availability of nitrogenous compounds might have limited microbial activity, particularly for CG and FT as suggested by their lower ruminal ammonia N levels at earlier times. In support, total VFA concentrations at 0 and 2 h were lower for CG and FT compared with CT and FI, and total VFA concentration at 4 and 6 h was numerically lowest among treatments for CG. Thus, energy avail-ability for CG doelings may have been lowest among treatments, and restricted microbial protein synthesis is possible as well. In accordance, in a separate Latin square experiment with adult Angora wethers fed the same diets (our unpublished observations), ADF digestibility was lowest among treatments for CG (34, 39, 44 and 48% for CG, CT, FT and FI, respec-tively). Similarly, in other instances supplementation of diets high in protein sources not extensively degraded in the rumen with urea or protein highly degradable in the rumen has increased ruminal micro-bial growth, digestibility and (or) ruminant perfor-mance (Church et al., 1982; Aderibigbe and Church, 1983; Cecava et al., 1990; Lu et al., 1990; Sahlu et al., 1992).
4.2. ADG and ®ber growth
In general, nutritional plane has affected ®ber growth and ADG similarly (Reis and Sahlu, 1994); however, such effects may depend on the nature of diets and animal characteristics. For example, in some Table 3
Effects of dietary protein source on ruminal ¯uid ammonia N and volatile fatty acid and concentrationsa
Item Dietb S.E.
Propionate 27 27 27 26 1
Butyrate 9.5 a 7.4 b 8.3 b 7.3 b 0.4 Valerate 1.17 1.04 1.17 1.11 0.07 Isovalerate 0.9 b 1.0 b 1.0 b 1.6 a 0.1 Isobutyrate 0.44 b 0.45 b 0.55 a 0.53 a 0.02 Acetate:propionate 2.5 2.4 2.4 2.7 0.3
aWithin a row, means without a common letters differ (P<0.05). bCG: corn gluten meal; CT: cottonseed meal; FT: hydrolyzed
instances an increased dietary level of ruminally undegraded protein has increased ¯eece growth with-out change in ADG (Sahlu et al., 1992; Huston et al., 1993). Likewise, in Merino sheep fed a roughage-based diet, FT supported a more rapid rate of wool growth than did CT but lower ADG (Neutze, 1990).
4.2.1. CG and ®ber growth
Factors responsible for greatest clean mohair growth rate for doelings consuming the CG diet, yet greatest ADG for FI doelings are unlcear. Although, a plausible explanation for greatest ®ber growth by CG doelings was alluded to earlier. Perhaps ruminal avail-ability of nitrogenous compounds limited VFA pro-duction and, thus, energy absorption to the greatest extent among treatments for CG. The amount of energy required by skin for ®ber growth is much less than that for peripheral muscle protein synthesis and maintenance (Harris and Lobley, 1991). In sheep, near maximal rates of wool growth can be sustained with use of a quantity of energy less than 5% of the basal metabolic rate (Black, 1987). Therefore, an energy limitation for CG that restricted nutrient use in per-ipheral muscle and(or) fat accretion may have caused nutrient partitioning to skin and increased ®ber growth (Harris and Lobley, 1991). The response to CG in ¯eece weight growth implies that the pro®le of avail-able amino acids was suitavail-able for use in ®ber growth. In accordance, greater ®ber growth for CG than for FT could relate to a more favorable array of amino acids available for use in ®ber growth, such as suggested by high supplemental protein source intakes of leucine and methionine for CG (leucine: 10.9, 3.8, 5.2 and 4.9 g/day; methionine: 1.7, 1.1, 0.7 and 1.9 g/day for CG, CT, FT and FI, respectively). Also, intestinal availability of amino acids in the protein supplements is unknown. Nonetheless, in the separate Latin square experiment referred to earlier (our unpublished obser-vations), apparent total tract CP digestibility was 77, 71, 62 and 79% for CG, CT, FT and FI, respectively. This suggests lowest intestinal digestibility among protein supplements for FT, which is in agreement with ®ndings of Calsamiglia et al. (1995).
4.2.2. FI and ADG
Ruminal ammonia N and VFA concentrations for FI do not indicate that ruminal microbial growth or digestion was restricted or limited by ruminal
avail-ability of nitrogenous compounds to the same degree as with CG. Thus, energy absorption might have been greater for FI versus CG and FT, and microbial protein synthesis may have differed as well. Greater energy availability could have allowed increased nutrient partitioning to ADG relative to conditions with CG and FT. Also, it is possible that the pro®le of absorbed amino acids elicited by dietary inclusion of FI was more favorable for ADG than that for CT, as indicated by relatively high supplemental protein source intakes for ®sh meal of lysine (0.9, 2.5, 1.5 and 4.6 g/day for CG, CT, FT and FI, respectively) and methionine.
5. Conclusions
Results of this experiment indicate that dietary characteristics promoting high growth or BW gain may not be those most conducive to high mohair growth. In this particular instance, a diet with supple-mental ®sh meal resulted in greater ADG than diets with feather, corn gluten or cottonseed meals, whereas corn gluten meal yielded greatest mohair growth. Further research is necessary to fully understand how dietary properties and nutrient status affects BW gain and mohair growth by yearling Angoras.
Acknowledgements
This research was supported by Project No. OKLX-2000-01.
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