Relationships among behavior, physiological states and body weight gain in grazing Holstein heifers

This study examined the behavior of dairy heifers and the factors affecting the performance of them on pasture. Behavior of 10 Holstein heifers in a herd of 25 animals that rotationally grazed five 8-ha pastures was observed and recorded every 5 minutes during 24 hours; body weights were measured once a month from June to October. Blood and rumen fluid samples were collected from 5 of them bimonthly. Chemical composition was analyzed for the forage samples collected each month. CP content (DM basis) of herbage ranged from 12.2 (June) to 17.2% (October) and ADF from 31.1 (October) to 39.1% (July). Standing (posture) time was different significantly among months (p<0.001) ranging from 48.3 to 61.3% of 24 hours and was longer in July and August (61.3% and 58.3%, respectively) when ADF content of herbage was higher than in the other months. Grazing time which significantly differed among months (p<0.001) ranged from 29.1 to 41.6% of 24 hours and was shorter in June and September (29.1% and 33.0%, respectively) when ADF content was lower than in the other months. Average DG through the experiment period was 0.74 kg/day. August was the lowest in DG (0.41 kg/day) and the longest in rumination time and standing-rumination time among months. Animals of higher DG had a shorter standing time (r=-0.36, p<0.01) and a longer lying-rumination time (r=0.55, p<0.001) throughout the experiment. Total protein concentration in blood ranged from 9.04 to 9.64 g/dl and was negatively correlated with DG (r=-0.65, p<0.05). Phospholipid concentration of blood ranged from 119.66 to 156.40 mg/dl and was negatively correlated with DG (r=-0.57, p<0.05). VFA in rumen fluid, acetic acid proportion (ranging from 69.35 to 74.76%) and butyric acid proportion (ranging from 7.18 to 12.05%) showed significant differences among months (p<0.05, p<0.001, respectively). Butyric acid proportion was significantly related with DG (r=0.60, p<0.05).