Effect of feed restriction and subsequent re-alimentation on hormones and genes of the somatotropic axis in cattle.

The objective of this study was to characterize the effect of feed restriction and compensatory growth during re-alimentation on the functionality of the somatotropic axis. We blocked 60 bulls into one of two groups: 1) restricted feed allowance for 125 days (period 1) (RES, n = 30) followed by ad libitum feeding for 55 days (period 2) or 2) ad libitum access to feed throughout (ADLIB, n = 30). A growth hormone releasing hormone (GHRH) challenge was performed during each period. At the end of each period, 15 animals from each treatment were slaughtered and hepatic tissue collected. Hepatic expression of 13 genes of the somatotropic axis was measured by qRT-PCR. RES displayed a lower growth rate during period 1 (0.6 vs. 1.9 kg/day; P < 0.001), subsequently gaining more than ADLIB animals during period 2 (2.5 vs. 1.4 kg/day; P < 0.001). Growth hormone response to GHRH was not different between treatments at either time-point (P > 0.05); however, resultant plasma IGF-1 was lower in period 1 and greater in period 2 in RES animals (P < 0.05). Expression of IGFBP2 was higher (P < 0.01) and IGF1 (P < 0.001) and GHRIA (P < 0.05) lower in RES compared with ADLIB during period 1, with no difference evident in period 2 (P > 0.05). Collectively, the results of this study are consistent with uncoupling of the somatotropic axis following feed restriction. However, there is no evidence from this study that the somatotropic axis per se is a significant contributor to compensatory growth.

Consequences of protein supplementation for anorexia, expression of immunity and plasma leptin concentrations in parasitized ewes of two breeds.

The periparturient relaxation of immunity (PPRI) against parasites in ewes has a nutritional basis. We investigated whether ewes experience a reduction in food intake (anorexia) during PPRI and if the magnitude of anorexia is affected by host production potential and dietary protein supplementation. We also investigated whether nematode infection is linked to plasma leptin concentrations in periparturient ewes. The experiment was a 2 x 2 x 2 factorial design. Two breeds of twin-bearing/lactating ewes (Greyface cross, G (n 32) and Scottish Blackface, B (n 32)) were used. Half of the ewes were trickle infected with 30,000 larvae of the abomasal parasite Teladorsagia circumcincta per week and the other half were not. During the experiment, all ewes had ad libitum access to a low-protein diet that provided less protein than the recommended allowance. In addition, half of the ewes received a protein supplement that resulted in protein intakes that exceeded recommendations. Nematode infection resulted in a breakdown of immunity to parasites and a reduction in food intake in both breeds. The breeds differed in the extent of PPRI (G ewes having higher faecal egg counts than B ewes), but not in the magnitude of anorexia. Protein supplementation resulted in a reduction in faecal egg counts, but had no effect on the magnitude of anorexia. Plasma leptin concentrations changed significantly over time, but were not affected by protein supplementation or infection. It is concluded that infection with T. circumcincta in periparturient ewes results in anorexia that is not alleviated by protein supplementation and seems unrelated to plasma leptin concentrations.

Reduction of severe bovine serum associated matrix effects on carboxymethylated dextran coated biosensor surfaces.

Surface plasmon resonance (SPR) based biosensor technology has been widely used in life science research for many applications. While the advantages of speed, ruggedness, versatility, sensitivity and reproducibility are often quoted, many researchers have experienced severe problem of non-specific binding (NSB) to chip surfaces when performing analysis of biological samples such as bovine serum. Using the direct measurement of the bovine protein leptin, present in bovine serum samples as a model, a unique buffering system has been developed and optimised which was able to significantly reduce the non-specific interactions of bovine serum components with the carboxymethyl dextran chip (CM5) surface on a Biacore SPR system. The developed NSB buffering system comprised of HBS-EP buffer, containing 0.5M NaCl, 0.005% CM-dextran, pH 9.0. An average NSB reduction (n=20) of 85.9% and 87.3% was found on an unmodified CM5 surface and a CM5 with bovine leptin immobilised on the chip surface, respectively. A reduction in NSB of up to 94% was observed on both surfaces. The concentration of the constitutive components and pH of the buffer were crucial in achieving this outcome.