Interaction effects of dietary energy density and feed bunk space on performance and nutrient digestibility in Holstein heifers

Replacement heifers represent the future potential of the dairy industry; as such, the feeding strategy for dairy heifers is to rear these animals at a minimum economic and environmental cost without reducing their future lactation performance (Hoffman et al., 2007). The main concern for heifer rearing industry is typically the energy densities of the diet exceeding the requirements of heifers, and subsequently, increase weight gains and lead to over-conditioning (Hoffman et al., 2008). The limited space is another concern for farmers in which feed bunks are limited and animals have to compete to meet their nutrient requirements. We hypothesized that feeding a ration diluted by wheat bran and rice hull in different feed bunk spaces would allow dairy heifers to compete and control their ad libitum intakes, and to meet their nutrient requirements for maintenance and target growth rates. Thus, the objective of this study was to investigation of interaction effects of dietary energy density and feed bunk space on performance and nutrient digestibility in Holstein heifers.

Four primiparous and 4 multiparous mid lactation dairy cows were stratified by pre-experimental milk yield (23.5 ± 2.3 kg/d), protein yield (0.75 ± 0.066 kg/d), parity, and days in lactation (121 ± 10 d) into 4 groups of 2 in a 2 × 2 factorial, Latin square design (n = 8) to assess the effect of forage source and a supplementary methionine hydroxy analog on nitrogen (N) balance where low crude protein (CP) diets (13.3%) are offered. Fourteen dairy heifers with an average age of 12-16 months and an average weight of 363 ± 32.8 kg were stratified into 4 groups of 10 in a 2 × 2 factorial, completely randomized design with four treatments and four stall. The experiment period was 100 days. Two levels of energy were adjusted in formulating diets. A diet was formulated according to NRC (2001) requirements as high energy diet (1.32 Mcal/kg DM). For low energy diet, it was diluted by rice hull and wheat bran to meet 90% of NRC (2001) requirements for energy (1.20 Mcal/kg DM). The diets were isoenergetic and isonitrogenous. Treatments included: 1- Small space with low level of energy, 24 cm feed bunk space with diet including 1.20 MCal/kg energy; 2- Small space with high level of energy, 24 cm feed bunk space with diet including 1.32 MCal/kg energy; 3- Large space with low level of energy, 48 cm feed bunk space with diet including 1.20 MCal/kg energy; and 4- Large space with high level of energy, 48 cm feed bunk space with diet including 1.32 MCal/kg energy. Sampling from feed and orts was carried out at 30, 45, 60 and 70 days. The dry matter intake was daily recorded. Feces samples were taken on days 30, 60 and 90 and dried at 70 ° C for 72 h. Total tract digestibility coefficients were calculated based on the relative concentrations of nutrients and AIA as an internal marker in the feed and feces. Chemical analysis of sample was done according to AOAC (1990). Data were analyzed as a complete factorial design with 2 levels of feed bunk space and 2 levels of dietary energy levels design using the GLM procedures of SAS (version 9.4, SAS Institute Inc., Cary, NC).

Dry matter intake was higher for heifers fed diet with low energy (P