ABSTRACT
The objectives of this study were: (1) to evaluate feed efficiency indexes and their relationships with body measurements and blood and ruminal metabolites in the pre-weaning period; (2) to determine if such measurements can be used as feed-efficiency markers during the pre-weaning period. Holstein-Gyr heifer calves (n = 36), enrolled between 4 and 12 weeks of age, were classified into two residual feed intake (RFI) and residual body weight gain (RG) groups: high efficiency (HE; RFI, n = 10; and RG, n = 9), and low efficiency (LE; RFI, n = 10; and RG, n = 8). Calves were fed whole milk (6 L/day) and solid feed ad libitum. Body developments were measured weekly and feed intake (milk and solid feed) daily during the whole period. Blood samples were collected at 12 weeks of age and analyzed for glucose, insulin and ß-hydroxybutyrate (BHB). Samples of ruminal content were collected on the same day and analyzed for pH, NH3-N, and volatile fatty acids (VFA). Among the growth characteristics, only the initial hip width differed between the RFI groups, and withers height differed between the RG groups. Concentration of BHB was greater and glucose: insulin ratios tended to be greater in LE-RG animals. Butyric acid proportions were similar among RFI groups, but tended to be greater for HE-RG than for LE-RG. Overall, correlation coefficients between RFI or RG and blood, rumen, or morphometric markers were low. Thus, it is unlikely that measurements of metabolic indicators, per se, will be useful in the early identification of more efficient animals. Understanding the underlying physiological basis for improved feed efficiency in dairy heifers requires further investigation.
ABSTRACT
Avaliaram-se os efeitos de diferentes níveis de inclusão (0, 100, 200 e 300g kg-1 de MS) de torta de macaúba (TM) na produção leiteira e no comportamento ingestivo de oito vacas Holandesas, em dois quadrados latinos 4x4, sendo quatro tratamentos e quatro períodos experimentais. O comportamento ingestivo foi determinado mediante observações visuais, ocorridas durante 24 horas, a intervalos de 5 minutos, para determinação do tempo despendido em alimentação, ruminação e ócio. Embora tenha ocorrido redução quadrática no consumo de matéria seca e na produção de leite com a inclusão de TM nas dietas, a eficiência alimentar (gMS h-1 e gFDN h-1) e a eficiência de ruminação (gMS h-1 e gFDN h-1) foram semelhantes em todos os tratamentos. O tempo total de mastigações (min dia-1), o número de bolos ruminados (n° dia-1), o número de mastigações merícicas (n° dia-1 e n° bolo-1) e o tempo de mastigações merícicas por bolo (seg bolo-1) não apresentaram diferenças. Os resultados permitem concluir que a inclusão da torta de TM na dieta de vacas leiteiras não influencia no comportamento ingestivo dos animais, entretanto, compromete o seu desempenho.
The effects of the macauba meal (MM) inclusion (0, 100, 200 and 300g kg-1 of DM) upon daily milk production and ingestive behavior parameters were evaluated in eight Holstein cows. Animals were randomly allocated to treatments according to a replicated latin square design, with four treatments and four experimental periods. The ingestive behavior was determined by observation, during 24 hours with 5 minutes intervals to determine the time spent in feeding, rumination and idleness. There was a quadratic decrease in dry matter intake and daily milk production with MM inclusion. However, no effects were detected in MM inclusion on the feeding efficiency (gDM h-1 and gNDF h-1) and rumination efficiency (gDM h-1 and gNDF h-1). The total chewing time (min day-1), the number of ruminated (boli day-1), the ruminating chews (n. day-1 and n. boli-1) and the time of ruminating chews boli (sec boli-1) did not show any difference. The MM inclusion in the diet did not influence the ingestive behavior, but reduces the performance of animals.
