Use of Methionine Supplements to Enhance the Protein Fraction of Goat Milk PDF Download

Author: Krista Lauren Jacobsen
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ISBN: 9781339064833
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Languages : en
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Book Description
The effects of dietary methionine supplements were studied using six lactating does (3 Saanen and 3 Alpine) all expressing alleles for low levels of alpha s1 casein (E/E or E/F) in a replicated Latin square design. Does were fed a basal diet composed of (as a proportion of total dry matter) 56.2% long alfalfa hay, 14.3% alfalfa pellets, and 29.5% concentrate ingredients. Methionine was fed either in the free form (not rumen protected) or rumen-protected to provide an additional 2.3 g methionine/doe daily. Other than effects on animal production performance, milk was analyzed for processing characteristics (rennet clotting time, firmness of rennet-induced gel, cheese yield and firmness), as well as proteomic profile to establish potential relationships between milk proteins, milk urea nitrogen, amino acid contents of plasma and milk, and milk fatty acid profile. Animal Production Results: Average daily milk yield and milk yield as a proportion of body weight (g milk/kg body weight) were improved relative to control by rumen-protected methionine in Saanens (p=0.03, both responses). Relative to control, plasma methionine increased with both supplements, but was only significant for the free-form treatment (p=0.05). Other amino acids (plasma and milk), urea nitrogen (plasma and milk), and content and yield of individual milk components were not affected by methionine supplementation, although a tendency was observed for increased yield of milk protein with methionine supplementation. Of the fatty acids measured in milk, concentrations of C9:0 and C11:0 were increased relative to control with the free-form methionine supplement in Saanens (p=0.02, each fatty acid). Rumen-protected methionine increased yield of C13:0 (p=0.04), compared to control. Yield of C15:0 was increased in Saanen milk with both the free-form (p=0.02) and rumen-protected (p=0.03) supplements, compared to control, and Alpines overall produced higher yields of C9:0 (p=0.04). Concentrations of C16:1 cis, C18:1 cis 11, C18:1 cis 13, and C22:5n3 were higher in Saanen milk while Alpine milk was higher in concentration of C18:2 cis 9 trans 11. Rumen-protected methionine tended to enhance daily yield of total casein; otherwise daily yields of individual caseins, as well as major whey proteins, were not affected by either treatment or breed. Milk Processing Results: Both rennet clotting time (p=0.02) and gel firmness (p=0.02) were improved by rumen-protected methionine, most notably among Saanens. Saanen milk tended to be higher in concentration of alpha s2 casein, alpha-lactalbumin, and lipoprotein lipase, but yields of these proteins did not differ from yields in Alpine milk. Mixed model selection revealed that increasing alpha s2 casein concentration improved rennet clotting time and cheese yield, whereas concentrations of C16:0 prolonged rennet clotting time. Milk urea nitrogen negatively impacted cheese firmness and yield, as well as concentrations of immune proteins in milk. The principal factors influencing concentrations of caseins and major whey proteins were plasma Group 1 amino acids (methionine, phenylalanine, tyrosine, tryptophan, and histidine) and plasma ornithine. Concentrations of butyrophilin and adipophilin were negatively influenced by concentrations of alpha s2 casein and positively by concentrations of kappa casein. Milk Proteomic Profile Results: Liquid chromatography tandem mass spectrometry analysis identified a total of 367 proteins in milk samples, with quantification achieved using intensity-based absolute quantification (iBAQ). Of the most frequently-detected proteins (i.e., in at least 12 out of 18 samples), the top primary function groups represented were immune/stress response (29.2% of the proteins), protein synthesis/folding (22.3%), transport/trafficking (16.9%), and lipid secretion/metabolism (6.9%). These results indicate that Saanens responded better than Alpines to methionine supplementation, and proportions of caseins, rather than concentration of milk protein alone, are important considerations when selecting goat milk intended for cheese production. The complete proteomic profile of whole goat milk contributes to a relatively sparse database. Knowledge of the types of proteins present in goat milk and their relative abundance can lead to the translation of their health promoting benefits.