Juan G. Magaña-Monforte

Genetic parameters for birth weight, weaning weight and age at first calving in Brown Swiss cattle in Mexico

Heritabilities and genetic correlations between birth weight (n = 13,741), adjusted 240-day weaning weight (WW, n = 8,806) and age at first calving (AFC, n = 3,955) of Brown Swiss cattle in Mexico were estimated. Data from 91 herds located in 19 of 32 states of Mexico from 1982 to 2006 were provided by the Mexican Brown cattle Breeder Association. Components of (co)variance, direct and maternal heritabilities were estimated for birth weight, WW and AFC using bivariate animal models. Direct and maternal heritabilities were 0.21 and 0.05 for birth weight, 0.40 and 0.05 for WW, whereas direct heritability for AFC was 0.08. The correlations between direct and maternal effects for birth weight and WW were −0.49 and −0.64, respectively. The genetic correlations between birth weight–WW and WW–AFC were 0.36 and −0.02, respectively. Under the conditions of this study, selection for increasing birth weight would increase WW, but increasing WW will not change AFC.

Perfiles sanguíneos de progesterona y estradiol del Pecari tajacu en cautiverio

The objective was to characterize the levels of progesterone (P4) and 17b estradiol (E-17b) in blood of 11 Pecari tajacu adult females in captivity. The females were in the presence of males but separated by a wire mesh. Blood samples were taken every 6 days during 3 months. The estimation of the levels of the steroid hormones was carried out by radioimmunoassay in solid phase. Hormonal profiles were plotted against time, to determine the duration of each ovarian cycle and the number of cycles. Nine animals showed estrous cycle and 2 did not. The average duration of the ovarian cycle was 26.8±4.8 days. The average concentration of P4 in the luteal phase was 22.95±4.94 ng/mL, and during the follicular phase was 1.2±0.73 ng/mL (p<0.05). The levels of E-17b in the luteal phase were 6.89±2.79 pg/mL, and 32.17±7.29 pg/mL in the follicular phase (p<0.05). The presence of the ovarian cycles was variable, although the duration was within the range of values established for this species under captivity. The synchrony of the hormonal profiles of P4 and E-17b during the ovarian cycle was inverted.

Effect of metabolizable energy intake on energy partitioning into muscle and fat in Pelibuey ewes

In ruminants, seasonality and physiological conditions result in fluctuations in feed intake, inducing periods of underfeeding and refeeding throughout the year. These seasonal variations induce fluctuations in live weight in grazing animals (Atti et al., 2000; Mahouachi and Atti, 2005; Kamalzadeh et al., 2009), and consequently in the energy content of the carcass and the whole body. Nonetheless, in hair sheep breeds there is scarce information relative to carcass composition and energy changes in the carcass during periods of weight loss and gain. Moreover, it has been reported that knowledge of body composition of productive animals is of relevance in order to better assess nutrient requirements. The aim of the present work was to evaluate the effect of metabolizable energy intake (MEI) on energy partitioning of muscular and adipose tissues in adult Pelibuey ewes.