Variation in sire genetics is an irrelevant determinant of digestibility in supplemented crossbred sheep

Malau-Aduli, Aduli, Walker, R.E., Sykes, J.M., Ranson, C.F., and Bignell, C.W. (2009) Variation in sire genetics is an irrelevant determinant of digestibility in supplemented crossbred sheep. In: Chilliard, Y., Glasser, F., Faulconnier, Y., Bocquier, F., Veissier, I., and Doreau, M., (eds.) Ruminant Physiology: proceedings of the XIth international symposium on ruminant physiology. Wageningen Academic Publishers, Clermont-Ferrand, France, pp. 278-279.

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The efficiency with which sheep produce meat and/or wool relies on a combination of available high quality nutrition and good genetics, hence the constant quest for sheep breed combinations that best utilise feeds to the maximum. High digestibility and nutrient retention of feed on offer are important indices of protein and energy available for wool fibre synthesis or muscle accretion in sheep. Both wool fibre number and diameter are strongly genetically determined. To our knowledge, it has not yet been established if sire genetics alone influences the digestibility and nutrient retention of dietary energy and protein in supplemented crossbred sheep. Therefore, the objective of this study was to evaluate the influence of sire genetics, dietary protein supplement type, level of feeding, sex and their second order interactions on metabolisable energy and nitrogen digestibility in first cross progeny of Merino dams sired by 5 ram breeds. Weaner sheep ( 40) sired by 5 ram breeds (Poll Dorset, Coopworth, Texel, East Friesian and White Suffolk), were balanced for liveweight (30 kg) and body condition score (3.0) on the average, before being randomly assigned to two supplementary feeds ( canola or lupins) and fed at two levels (1 % or 2.0% BW). The feeding trial lasted for six weeks including an initial adjustment period of 3 weeks and the final 1 wk of faecal and urinary collection. All treatment groups received a daily allocation of an isocaloric and isonitrogenous diet comprising 0.5 kg of barley, 0.1 kg molasses-treated straw and 0.001 kg vitamin-mineral mix at 10:00 h. Each sheep had ad libitum access to clean, drinking water. DM intake and output, body weight, and change in wool fibre diameter ( difference in wool microns at the beginning and end of the feeding trial) were measured. DM digestibilities were measured and data subjected to a general linear models procedure (PROC GLM) of the Statistical Analysis System® (SAS Institute, 2007) and significance established using orthogonal contrasts and Tukey pairwise comparisons. The model included sire breed, supplement, feeding level, sex as main effects and their second order interactions.

Regardless of sire genetics, feeding level or gender, sheep supplemented with canola consumed 4.5% more feed (DMI 163.5 vs. 149.2 g/day), voided 17% more faeces (51.08 vs. 35.97 g/day), digested 8.5% more ME (52.23 vs. 44.23%) and had 4% heavier liveweights (40 vs. 36.9kg) than those supplemented with lupins. Feeding supplements at 1 % of body weight triggered higher ME (49.9% vs. 46.5%) and N (64.9% vs. 63.2%) digestibility responses than feeding at 2%. There was a tendency for females to eat more than males (161.8 vs. 149.6 g/day DMI]) and N digestibility was 2% higher in males (65%) than females (63%). Sire genetics x level of feeding interactions significantly influenced ME and N digestibility (P<0.05) whereby Coopworth-sired sheep supplemented at 1 % of their body weight recorded the highest ME and N digestibility of S4% and 67% compared to 42% and 62% respectively, than their counterparts fed at 2% of body weight. There was a highly significant (P<0.01) effect of type of supplement x level of feeding interaction on wool fibre diameter because sheep fed canola supplements at 1 % of body weight bad finer wool (22.1 microns) than their 2%-fed counterparts (25.4 microns).

The post-ruminal delivery of nutrients in sheep supplemented with canola was more efficient than in lupin-supplemented sheep, hence their higher energy and protein digestibility and retention. Furthermore, variation due to sire genetics alone was insufficient in accounting for differences in digestibility and wool fibre diameter, but significantly interacted with type of supplement; level of feeding and sex .. Finally, sire breed variation in digestibility is unlikely to be a useful predictor of genetic merit for wool fibre diameter in first cross sheep.

Item ID: 55052
Item Type: Book Chapter (Scholarly Work)
ISSN: 978-90-8686-119-4
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Presented at the XIth International Symposium on Ruminant Physiology, 6-9 September 2009, Clermont-Ferrand, France

Date Deposited: 05 Mar 2019 01:13
FoR Codes: 07 AGRICULTURAL AND VETERINARY SCIENCES > 0702 Animal Production > 070201 Animal Breeding @ 50%
07 AGRICULTURAL AND VETERINARY SCIENCES > 0702 Animal Production > 070204 Animal Nutrition @ 50%
SEO Codes: 83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8303 Livestock Raising > 830310 Sheep - Meat @ 100%
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