Effect of lactation and breed on reproductive cyclicity under various states of oxidative stress in dairy cattle breeds

This study was carried out to study effects of lactation and breed on reproductive cyclicity under various states of oxidative stress in dairy cattle. different parameters including body condition score (bcs),daily milk yield (dmy),glucose,malondialdehyde (mda),cortisol and progesterone were analysed to see the association of these parameters with postpartum days and breeds. thirty-six periparturient lactating dairy cows,nine each from sahiwal,achai,holstein frisian (hf) and cross (sahiwal x hf) breed were selected. blood sample were collected on post-partum day (ppd) 60,82 and 105 of the lactation stage during diestrus. dmy varied significantly with ppds and within breed (p<0.001). interaction between ppds x breed was highly significant (p<0.01) for dmy. serum glucose and progesterone level significantly increased with increase in ppds (p< 0.01) while mda and cortisol level decreases with increase in ppds in all breeds. moreover breed also significantly affected glucose (p< 0.001) and mda concentrations. bcs was negatively correlated with serum cortisol,glucose and progesterone. cortisol,dmy and mda were positively correlated with each other and negative with progesterone and ppds. the study revealed that hf and cross-bred dairy cows were more prone to oxidative stress than local breeds. correlation analysis indicates that higher yield is associated with reduced reproductive performance in lactating cows,primarily through delayed ovarian activity as assessed by reduced progesterone concentrations during high milk production phase,suggesting that high milk producers should be provided with extra-managemental support for better productivity and fertility. © copyright 2016 zoological society of pakistan.