Milk yield and quality, nitrogen metabolism and rumen fermentation parameters in dairy cows fed different level of dietary concentrate and live yeast

Abstract

The overall objective of this study was to investigate the effects of level of dietary concentrate and live yeast (LY) on milk yield, milk composition, rumen fermentation and nitrogen metabolism in lactating dairy cows. Four primiparous Holstein dairy cows in early lactation (average weight 500 ±9 kg and 20 days in milk (DIM)) were used in a 4 x 4 Latin Square design for a period of 44 days. The animals had seven days of adaptation to the treatments and four days for measurements. The treatments were, Low concentrate to forage (C:F) diet (40:60) with no additive, High C:F diet (60:40) with no additive, High C:F diet with LY and Low C:F diet with LY.Cows weremilked at 06h00 and 16h00 daily and milk samples were analysed for fat, protein, lactose milk urea nitrogen (MUN) and somatic cell count (SCC). Proximate analysis of feed samples was done and daily feed intake was recorded. Weight and body condition score were determined at beginning and end of every experimental period. Faecal and urinary nitrogen (N)were determined. In vitro batch fermentation was conducted to determine ruminal fermentation kinetics. Data generated from the feeding trial was analysed for a 4 x 4 Latin square design (LSD) using the PROC MIXED procedure of SAS (2009) and data for the invitro trialwassubjected to ANOVA using PROC GLM (SAS Institute, 2009) for a complete randomized design. Addition of LY affected only dry matter intake (DMI) (P<0.05), which effect was pronounce when cows were fed low (40:60) C:F diet resulting in better feed efficiency(FE). Cows fed high C:F diet consumed more feed, produced more milk with high fat and protein content (P<0.05). Both LY and C:F reduced (P<0.05) N intake as result of low DMI, but reduced (P<0.05) N excretion in manure. Addition of LY decreased ruminal ammonia and increased total VFA’s (P<0.05). The effects on ammonia suggest a better utilisation of diet proteins and probably more incorporation of products of CP degradation into microbial proteins, which support the observed reduced manure N excretion. The opposite was observed with high C:F diet, which increased ammonia and decreased total VFA’s. Propionate and butyrate were increased and decreased, respectively by high C:F diet.Addition of LY reduced SCC and MUN compared to control.The effects of LY were better pronounced on most parameters at low C:F diet. It is therefore recommended that the effects of LY be tested at low C:F on a larger scale of animals over longer periods to observe its effect of the rest of the parameters.