Effects of induced subacute ruminal acidosis and laminitis on lipopolysaccharide binding protein, cortisol and progesterone levels in dairy heifers

Abstract

Subacute ruminal acidosis (SARA) is a predisposing cause of laminitis and results in an inflammatory response in dairy cattle. However, the link between SARA associated with laminitis and inflammation and the endocrinal profiles related to reproduction has not been clearly demonstrated. This study was conducted to investigate the effects of high concentrate-induced SARA and laminitis on the changes in lipopolysaccharide binding protein (LBP), cortisol and progesterone in dairy heifers. Six treated heifers were induced by feeding concentrate ad libitum with restricted amounts of rice straw (1 kg DM/day), while six control heifers were restrictively fed amounts of concentrate (2.2 kg DM/day) and fed rice straw ad libitum. Ruminal fluid collection, blood sampling, hoof testing and reproductive examinations were performed during 8 days of the experimental period. SARA (ruminal pH < threshold value, 6.00) and hoof pain were detected in the treated heifers from days five to eight of the experimental period. SARA and hoof pain were not detected in any control heifers. Means of plasma LBP and cortisol of the treated heifers were significantly higher (p < 0.05) than those of the control heifers. Serum progesterone levels which increased during 36 to 72 h after ovulation in the treated heifers were significantly lower (p < 0.05) than those in the control heifers. These results suggested that feeding high levels of concentrate induced SARA which caused laminitis and resulted in an inflammatory response. The hoof pain and inflammation led to increased cortisol hormone. These circumstances had a suppressive effect on the increase of serum progesterone levels after ovulation.