Effects of dietary protein concentration and coconut oil supplementation on nitrogen utilization and production in dairy cows

Abstract

The objective of this study was to investigate the effect of metabolizable protein (MP) deficiency and coconut oil supplementation on N utilization and production in lactating dairy cows. The hypothesis of the study was that a decrease in ruminal protozoal counts with coconut oil would increase microbial protein synthesis in the rumen, thus compensating for potential MP deficiency. The experiment was conducted for 10 wk with 36 cows (13 primiparous and 23 multiparous), including 6 ruminally cannulated cows. The experimental period, 6 wk, was preceded by 2-wk adaptation and 2-wk covariate periods. Cows were blocked by parity, days in milk, milk yield, and rumen cannulation and randomly assigned to one of the following diets: a diet with a positive MP balance (+44 g/d) and 16.7% dietary crude protein (CP) concentration (AMP); a diet deficient in MP (-156 g/d) and 14.8% CP concentration (DMP); or DMP supplemented with approximately 500 g of coconut oil/head per day (DMPCO). Ruminal ammonia tended to be greater and plasma urea N (20.1, 12.8, and 13.1 mg/dL, for AMP, DMP, and DMPCO diets, respectively) and milk urea N (12.5, 8.3, and 9.5mg/dL, respectively) were greater for AMP compared with DMP and DMPCO. The DMPCO diet decreased total protozoa counts (by 60%) compared with DMP, but had no effect on the methanogens profile in the rumen. Total tract apparent digestibility of dry matter and CP was decreased by DMP compared with AMP. Fiber digestibility was lower for both DMP and DMPCO compared with AMP. Urinary N excretion was decreased (by 37%) by both DMP and DMPCO compared with AMP. The DMP and DMPCO diets resulted in greater milk N efficiency compared with AMP (32.0 and 35.1 vs. 27.6%, respectively). Milk yield was decreased by both DMP and DMPCO compared with AMP (36.2, 34.4, and 39.3 kg/d, respectively) and coconut oil supplementation suppressed feed intake and caused milk fat depression. Coconut oil supplementation decreased short-chain fatty acid (C4:0, C6:0, and C8:0) concentration and increased medium-chain (C12:0 and C14:0) and total trans fatty acids in milk. Overall, the MP-deficient diets decreased N losses, but could not sustain milk production in this study. Coconut oil decreased feed intake and similar to DMP, suppressed fiber digestibility. Despite decreased protozoal counts, coconut oil had no effect on the methanogen population in the rumen.

Rumen microbial community and nitrogen metabolism in goats fed blend of palm oil and canola oil

“…Rumen protozoa are predators of bacteria (Mao et al 2010;Liu et al 2012). The consumption and digestion of bacteria by rumen protozoa is a wasteful process, which causes undesirable recycling of nitrogen in the rumen (Lee et al 2011).…”

“…This observation is similar to that of Mao et al (2010) who observed that dietary soybean oil reduced the population of methanogens in lambs. Rumen protozoa are implicated in methane production because of the endo-and ecto-symbiotic relationships between rumen protozoa and methanogens (Lee et al 2011). The reduction in the population of protozoa and methanogen in oil-supplemented goats lends credence to the reduction in the methane concentration in the goats (Adeyemi et al 2016).…”

“…Nonetheless, unsaturated fats could have detrimental effect on rumen microbial ecology (Mao et al 2010), which could affect fibre digestibility and voluntary feed intake in ruminants. The impact of lipid supplementation on rumen microbiota in sheep (Mao et al 2010) and cattle (Lee et al 2011;Ivan et al 2013) has been documented. However, similar in vivo studies are seldom reported for goats.…”

“…A shortfall in N supply or excess N beyond its basal requirements could have environmental and economic consequences (Lee et al 2011). Thus, optimising N efficiency to reduce production cost and limit environmental pollution is warranted.…”

“…Thus, optimising N efficiency to reduce production cost and limit environmental pollution is warranted. One major strategy for enhancing N efficiency is increasing ruminal microbial protein synthesis, which can be maximised by defaunation (Doreau & Ferlay 1995;Lee et al 2011). Dietary fat can reduce the population of rumen protozoa (Mao et al 2010;Ivan et al 2013).…”