Effects of total replacement of corn silage with sorghum silage on milk yield,composition, and quality

Background： In the last years, difficulties occurring in corn cultivation（i.e., groundwater shortages, mycotoxin contamination） have been forcing dairy farmers to consider alternative silages. Some experiments conducted on lactating cows have proven that the total replacement of corn silage with sorghum silage did not reduce milk yield.However, this kind of substitution involves supplementing sorghum-based diets with grains, to compensate for the lower starch content of sorghum silage compared to corn silage. Change of silage type and inclusion of starch sources in the diet would influence rumen fermentations, with possible effects on milk composition（i.e., fatty acid profile） and coagulation properties. A worsening of milk coagulation properties would have a negative economic impact in Italy, where most of the milk produced is processed into cheese.This study was designed to compare milk composition and quality, with emphasis on fatty acid profile and coagulation properties, in dairy cows fed two diets based on corn or sorghum silage.Results： The sorghum diet reduced milk yield（P = 0.043） but not 4% fat corrected milk（P = 0.85）. Feeding sorghum silage did not influence milk contents of protein（P = 0.07） and lactose（P = 0.65）, and increased fat content（P = 0.024）.No differences emerged for milk concentrations of saturated（P = 0.61） and monounsaturated fatty acids（P = 0.50）,whereas polyunsaturated fatty acids were lower（P 〈 0.001） for the sorghum diet. Concentrations of n-6（P 〈 0.001） and n-3 fatty acids（P = 0.017） were lower in milk of cows fed the sorghum diet. Milk coagulation properties did not differ between the two diets, except the ＂a30＂（the curd firmness, expressed in mm, 30 min after rennet addition）, that was lower（P = 0.042） for the sorghum diet.Conclusions： Feeding a forage sorghum silage, properly supplemented with corn meal, as total replacement of corn silage maintained milk composition and did not influence negatively milk coagulation properties, which have a great economic relevance for the Italian dairy industry. Thus, silages obtained from forage sorghums could have a potential as substitute of corn silages in dairy cow diets.

Physiological and Biochemical Characteristics of Lactation in Half-lactating Yak

Yaks of two lactating types, the half-Iactating yak and the total lactating yak, were investigated in their milk compositions, milk coagulation properties, and contents of three kinds of hormones, glucose, and protein in plasma. The half-lactating Maiwa yak and Jiulong yak contained significantly higher contents of protein, fat, and activities of alkaline phosphatase and Y-glutamyl transpeptidase in milk than that of the corresponding total-lactating yak breeds, with reduced milk yield and similar lactose level and relative percentages of main milk protein components. The half-lactatin yak resembled yaks in a late stage of lactation in their biochemical composition of milk; however, significant differences were also observed, which indicated that the former was in a special stage of lactation quite different from dairy cows. Milk of the total-lactating or half-lactating yaks could be coagulated normally by adding chymosin, with a similar coagulation time. No significant difference was observed between prolactin and progesterone concentrations in plasma of the half-lactating yaks and total-lactating yaks; however, half-lactating yaks had significantly lower level of oestradiol-17 β in plasma than total-lactating yaks.

Optimum Production and Characterization of an Acid Protease from Marine Yeast Metschnikowia reukaufii W6b

The marine yeast strain W6b isolated from sediment of the South China Sea was found to produce a cell-bound acid protease.The crude acid protease produced by this marine yeast showed the highest activity at pH 3.5 and 40 ℃.The optimal pH and temperature for the crude acid protease were in agreement with those for acid protease produced by the terrestrial yeasts.The optimal medium of the acid protease production was seawater containing 1.0% glucose, 1.5% casein, and 0.5% yeast extract, and the optimal cultivation conditions of the acid protease production were pH 4.0, a temperature of 25 ℃ and a shaking speed of 140 rmin-1.Under the optimal conditions, 72.5 UmL-1 of acid protease activity could be obtained in cell suspension within 48 h of fermentation at shake flask level.The acid protease production was induced by high-molecular-weight nitrogen sources and repressed by low-molecu-lar-weight nitrogen sources.Skimmed-milk-clotting test showed that the crude acid protease from the cell suspension of the yeast W6b had high skimmed milk coagulability.The acid protease produced by M.reukaufii W6b may have highly potential applications in cheese, food and fermentation industries.