Reducing dietary crude protein: Effects on digestibility, nitrogen balance, and blood metabolites in late-lactation Holstein cows

ABSTRACT: Our objectives were to determine the effects of reducing dietary CP concentration on nutrient digestibility, rumen function, N balance, and serum AA concentration for dairy cows in late lactation. At the initiation of the experimental period, we stratified Holstein cows (n = 128; mean ± SD 224 ± 54 DIM) by parity and days pregnant (86 ± 25 d) and assigned them to 1 of 16 pens. For 3 wk, all cows received a covariate diet containing 16.9% CP (DM basis). For the subsequent 12 wk, we assigned pens to 1 of 4 treatments containing 16.2%, 14.4%, 13.4%, or 11.9% CP (DM basis) in a randomized complete block design. Diets were fed as a TMR once daily. To reduce dietary CP, we replaced soybean meal with soybean hulls in the concentrate mix (DM basis). Diet evaluations suggested that several EAA, especially His, limited productivity as dietary CP declined. Digestibility of DM and CP decreased linearly with dietary CP reduction. Digestibility of NDF and potentially digestible NDF tended to respond in a quadratic pattern with the greatest digestibility at intermediate treatments. The reduction in dietary CP did not affect ruminal pH, but ruminal ammonia-N and branched-chain VFA concentrations declined linearly. The concentration of milk urea-N and plasma urea-N, secretion of milk N, and excretions of fecal N, urinary N, urinary urea-N, and unaccounted N decreased linearly with the reduction in dietary CP concentration. Urinary N expressed as a percentage of N intake was unaffected by dietary CP. Serum concentrations of total essential AA and NEAA were unaffected by dietary CP concentration. However, the ratio of essential to NEAA decreased with decreasing dietary CP. Serum 3-methylhistidine concentration increased linearly with decreasing dietary CP concentration, indicating greater skeletal muscle breakdown. Although our trial confirmed that reducing dietary CP decreased absolute excretion of urinary N, diet evaluations suggested that milk protein production decreased as certain essential AA became increasingly limited. Thus, reduced-CP diets have the potential to lessen reactive-N outputs of late-lactation cows, but more research is needed to design diets that minimize deleterious effects on productivity

Effect of feeding a reduced-starch diet with or without amylase addition on lactation performance in dairy cows

The objective of this study was to determine lactation performance responses of high-producing dairy cows to a reduced-starch diet compared with a normal-starch diet and to the addition of exogenous amylase to the reduced-starch diet. Thirty-six multiparous Holstein cows (51 +/- 22 DIM and 643 +/- 49 kg of body weight at trial initiation) were randomly assigned to I of 3 treatments in a completely randomized design: a 3-wk covariate adjustment period during which the cows were fed the normal-starch diet, followed by a 12-wk treatment period during which the cows were fed their assigned treatment diets. The normal-starch TMR did not contain exogenous amylase (NS-). The reduced-starch diets, formulated by partially replacing corn grain with soy hulls, were fed without (RS-) and with (RS+) exogenous amylase added to the TMR. Starch and NDF concentrations averaged 27.1 and 30.6%, 21.8 and 36.6%, and 20.7 and 36.6% (dry matter basis) for the NS-, RS-, and RS+ diets, respectively. Dry matter intake for cows fed the RS- diet was 2.4 and 3.2 kg/d greater than for cows fed the NS- and RS+ diets, respectively. Intake of NDF ranged from 1.19 to 1.52% of body weight among the treatments, with the RS- diet being 28% greater than the NS- diet and 13% greater than the RS+ diet. Milk yield averaged 50.4 kg/d and was unaffected by treatment. Fat-corrected milk yield was 2.9 kg/d greater for cows fed the RS- diet than for cows fed the NS- diet. Body weight and body condition score measurements were unaffected by treatment. Fat, solids-, and energy-corrected milk feed conversions (kilograms/kilogram of DMI) were 12 to 13% greater for cows fed the RS+ diet than for cows fed the RS-diet. Dry matter and nutrient digestibilities were lowest for cows fed the NS- diet and greatest for cows fed the RS+ diet, and were greater for cows fed the RS+ diet than for cows fed the RS- diet, with the exception of starch digestibility, which was similar. Greater conversion of feed to milk for dairy cows fed reduced-starch diets that include exogenous amylase may offer potential for improving economic performance

Condição corporal e desempenho produtivo de cabras Alpinas no início de lactação Body condition and productive performance of Alpine goat in early lactation

Objetivou-se avaliar a influência da condição corporal ao parto sobre os parâmetros produtivos de cabras Alpinas no início da lactação. Sessenta e oito cabras foram distribuídas em três grupos, de acordo com o escore de condição corporal (baixo, entre 1,00 e 2,75; intermediário, entre 2,75 e 3,50; e alto, entre 3,50 e 5,00) e avaliadas do parto até a oitava semana de lactação. Realizaram-se o controle diário do consumo alimentar e da produção leiteira e avaliações semanais de peso corporal, escore da condição corporal e composição do leite. Os animais com escore corporal alto apresentaram menor consumo de matéria seca, fibra em detergente neutro e proteína bruta em comparação àqueles com escores corporais baixo e intermediário. O período médio de recuperação do consumo de matéria seca dos animais das três condições corporais foi de 16 dias (2,3 semanas) do pós-parto, com estabilização até o final do experimento. Na sexta semana de lactação, o peso corporal dos animais com escore corporal baixo se igualou ao daqueles com escore corporal intermediário. Não houve efeito da condição corporal ao parto nas variações de ECC e da produção leiteira ao longo do período. O teor de gordura do leite dos animais com escore corporal alto foi menor nas duas primeiras semanas pós-parto em comparação ao dos animais com escores corporais baixo e intermediário. Elevada condição corporal ao parto influencia negativamente o consumo voluntário de cabras leiteiras no início da lactação, mas quando se utiliza dieta de alta qualidade e com altos níveis de energia, a influência da condição corporal ao parto inexiste para variações de peso, de escore da condição corporal e produção leiteira dos animais.<br>The objective of this study was to evaluate the influence of body condition at birth on Alpine goat productive parameters in early lactation. Sixty-eight females were assigned to three groups according to the body condition score (BCS) - low (1.00 - 2.75); intermediate (2.75 - 3.50) and high (3.50 - 5.00) and evaluated from kidding to the eighth week of lactation. The feed intake and milk production were recorded on a daily basis and the body weight, body condition score and milk composition at weekly intervals. Animals with a high body condition score presented lower dry matter intake, neutral detergent fiber and crude protein compared to those with low and intermediate body condition scores. The average time for dry matter intake recovery of the animals with the three body condition scores was 16 days (2.3 weeks) postpartum, and stabilization by the end of the experiment. In the sixth week of lactation, animals with low body condition score had the same body weight of animals with intermediate body condition score. There was no effect of the body condition at birth on the body condition score changes and milk production during the experiment. The milk fat content of animals with high body condition score was lower in the first two weeks postpartum compared to animals with low and intermediate body condition score. The high body condition at birth influences negatively the ad libtum intake of dairy goats in the early lactation, but when it is used feed of high quality with high energy levels, the influence of the body condition at birth is nil to variations in weight, BCS and milk production