Comparative study on the regulation of body fluids and mammary circulationat different stages of lactation in crossbred Holstein cattle feeding on different types of roughage

The present study was carried out to evaluate the effect of prolonged feedi ng of urea-treated rice straw, compared with feeding of hay, on the regulat ion of body fluids, milk yield and mammary circulation at early lactation ( 30 days postpartum), mid lactation (120 days postpartum) and late lactation (210 days postpartum) in crossbred Holstein Friesians. Sixteen first lacta ting crossbred Holstein Friesians (HF), consisting of eight animals of two breed types, 87.5%HF and 50%HF, were selected and each breed was randomly a llocated into two groups. Each group, consisting of four animals from the s ame breed, was fed either 5% urea-treated rice straw or pangola hay (Digita ria decumbens) as the source of roughage in combination with a similar conc entrate throughout the experiments. During the course of lactation there we re no significant differences in body weight, heart rate, mean arterial blo od pressure, plasma osmolality, plasma volume and blood volume among groups of 87.5%HF animals and 50%HF animals fed either hay or urea-treated rice s traw. Water turnover rate, total body water space and total body water as a percentage of body weight of 50%HF animals were significantly higher than these of 87.5%HF animals fed either hay or urea-treated rice straw. The pac ked cell volume was significantly higher in all lactating periods of both g roups of 50%HF animals in comparison with 87.5%HF animals. The ratio of DM intake to milk production for 87.5%HF animals fed either hay or urea-treate d rice straw was significantly lower than that of 50%HF animals in early la ctation. The udder blood flow and milk secretion of 87.5%HF were significan tly higher in early lactation and markedly declined when lactation advanced in comparison with those of 50%HF animals fed either hay or urea-treated r ice straw. The ratio of mammary blood flow to milk yield for all groups was in a similar range during early lactation although it significantly increa sed in mid- and late lactation for both groups of 87.5%HF animals. From the se results it can be concluded that both 50%HF and 87.5%HF animals feeding on urea-treated rice straw as a roughage source do not show any undernutrit ional effects in comparison with those fed with hay during the course of la ctation. The physiological response differences between breeds are that 87. 5%HF animals, which have a genetic makeup closer to the exotic bos taurus b reed and a high milk yield, show a poor adjustment to the tropical environm ent and poorer lactation persistency in comparison with 50%HF animals.