Reduction of crude protein in diets fed to lactating Holstein-Gyr cows

Clóvis Ribeiro Guimarães,Luiz Gustavo Ribeiro Pereira,Sandra Gesteira Coelho,Luciano De Rezende Carvalheira,Fernanda Samarini Machado,Thierry Ribeiro Tomich,Rafael Alves De Azevedo,Mariana Magalhães Campos,Alexandre Mendonça Pedroso

doi:10.1590/s0100-204x2018000700010

Clóvis Ribeiro Guimarães, Luiz Gustavo Ribeiro Pereira + Show 7 more

Open Access

https://doi.org/10.1590/s0100-204x2018000700010

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Abstract

Abstract: The objective of this work was to evaluate the effect of reducing crude protein (CP) contents in diets with a constant metabolizable protein content on the intake, performance, nitrogen balance, and nutrient digestibility of lactating Holstein-Gyr cows. Animals (n = 24, 103±23 days in milk) were allocated to four treatments (n = 6 per group) with different CP contents: 127, 132, 139, and 156 g kg-1 dry matter (DM). DM intake was not affected by treatments. CP intake and digestibility increased linearly with higher CP contents. Milk yield (23.7±3 kg per day) and the percentages of milk protein (3.3±0.2%) and fat (3.8±0.5%) were not affected by CP reduction. Milk and blood urea nitrogen increased linearly with the increase of CP in the diet, similarly to urinary nitrogen excretion. Nitrogen use efficiency was 29.8 and 22.4% when CP was 127 and 156 g kg-1 DM, respectively. Reducing CP in diets fed to mid-lactating Holstein-Gyr cows increases nitrogen use efficiency and maintains the productive performance of the cows.

Highlights

The intensification of milk production systems and the pursuit of maximum economic efficiency are a worldwide reality
The intakes of dry matter (DM), neutral detergent fiber (NDF), acid detergent fiber (ADF), EE, and gross energy (GE) were similar among treatments (Table 2), possibly because the diets were isoenergetic and balanced to meet the metabolizable protein requirements of the HolsteinGyr cows
The digestibility of crude protein (CP) increased linearly according to the increase in its contents, probably due to a dilution effect, given that fecal nitrogen remained constant among treatments

Summary

Introduction

The intensification of milk production systems and the pursuit of maximum economic efficiency are a worldwide reality. With this focus, studies and investments have sought genetic improvement alongside herd nutrition to obtain highly productive animals. According to Law et al (2009), an increase in CP of up to 173 g kg-1 DM in the diets of early-lactating cows had beneficial effects on milk production and DM intake. For animals between 151 and 305 days in milk, the most efficient nitrogen use was achieved with lower CP contents of 144 and 173 g kg-1 DM in the diets, with no detrimental effects on production (Law et al, 2009).

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