EFFECT OF BOVINE SOMATOTROPHIN HORMONE ON MILK PRODUCTION IN DAIRY COWS GRASSING DURING RAINY SEASON. BUGABA, CHIRIQUI, PANAMA. 1997.

Abstract

The present experiment was carried out in a dairy farm located in Volcan area, Bugaba district, province of Chiriqui. The aim of the research was to determine the effect of bovine somatotrophine (BST) upon milk production in dairy cows grazing during rainy season. Two groups of Holstein cows were created with 35 each one (non pregnant cows, with different number of lactations, with an average of 106 lactation days). Treated group (T₁) received one injection of Lactotrophin^® (Monsanto Laboratories, Mexico F.D.) at 14 days intervalas, in the illiacus – anal región. A not treated group (T₂) was designed as control. All cows were milked twice a day and feeded with grass under a rotational grazing system and received 8 kg of an additional concentrate with 2500 Kcal/kg and 20% CP. For data analysis an aleatory design was adopted which included lactation numbers (NL), days of milking as covariable (DO) and finally, an Student test was applied to pared datas in the statistical model. Also a regression model (R) was used for analysis the speed of diminishing milk production between experimental groups. According with obtained results there were not statistical differences between groups T₁ and T₂. The Student test did not show any  significant differences in the analysis of pared samples (P>0.8954). The variation coeficient (28.42%) induce that there were not environment factors altering results and good control of experimental mistakes. The covariance NL did not evidenced any effect in the experiment, meanwhile DO was affected for the aplication of BST. The results obtained with the R, were well adjusted to the lineal model and the regression coefficient (CR), was highly significant (P<0.001). However CR for T₁ (0.0921) and T₂ (0.0802) were similar, indicating not differencess in the speed of diminishing milk production between groups. According with these results, we concluded that the application of STB hormone increased the milk production and lactation length in treated group, but the response was not economical respect to the not treated group.