Effect of suckling during early lactation and changeover to machine milking on plasma oxytocin and cortisol levels and milking characteristics in Holstein cows.

Plasma concentrations of oxytocin and cortisol, and milk yield and flow rates, were compared in three primiparous cows and two cows in their second lactation during suckling and subsequent machine milking. After calving, cows suckled their calves for 3-4 weeks and then the experiment was carried out over 4 d. Blood samples were taken prior to, during and after suckling or evening machine milking (EMM) on day 1 of the experiment (the last day of suckling), day 2 (first EMM) and day 4 (third EMM). After weaning and rehousing, cows were machine milked twice daily. During the first EMM, average milk yield and flow rate in the second minute of milking were significantly lower (P < 0.05) than corresponding values for the other 2 d. Plasma oxytocin concentrations were lower during the first than during the third EMM (P < 0.001) and suckling (P < 0.001), and more oxytocin was released during the third EMM than during suckling (P < 0.01). Cortisol concentrations were higher during and after the first EMM than during the third EMM. Thus in cows sucked for several weeks after calving and then separated from their calves and rehoused we found a transient decrease in oxytocin release, milk yield and flow rates during the first machine milking.

[Changes in oxytocin and cortisol levels in primiparous cows after changing from 21 days of suckling calves to machine milking]. / Zmeny hladiny oxytocínu a kortizolu u prvôstok po prechode z 21-dnového cicania tel'atami na strojové dojenie.

Four first-calvers of the Black-Pied breed with calves sucking their milk until day 21 of lactation were included in a trial. One suckler cow had four calves. The trial took place within five days which included days 20 and 21 in the first-calvers, that means the last two days with sucking calves (designated as day 1 and day 2 of trial-first and second calf sucking) and days 22 and 24, that means the first and third day after the cows were moved to a cowshed (designated as the third and fifth day of trial-first and third evening machine milking). The first-calvers were separated from the calves and moved to a cowshed at 8 o'clock a.m. on day 3 of trial (Tab. I). The responses to calf sucking were investigated after four-hour prevention of calves to approach the cows (12.00-16.00 p.m.). Blood was sampled with a catheter which was introduced into the vena jugularis a day before the trial outset. Blood samples for cortisol determination were taken in two-hour intervals (when the cows were moved to the cowshed twice in half-an-hour interval and once in an hour interval). Blood samplings were effectuated by day, before, during and after milking, or sucking. Machine milking was finished within 7 to 8 minutes. Two to four calves were intensively sucking a cow within the first 15 minutes, then sucking was irregular. Plasma samples were deep-frozen and stored at -20 degrees C until determinations were performed. Oxytocin and cortisol in the blood plasma were determined by radioassays. In the first evening machine milking (day 3) the second cow yielded 8.23 kg milk while on day 5 in the third milking it was 7.98 kg. The other first-calvers gave by 30-45% less milk on day 3 in comparison with evening milking on day 5 (Tab. II). A trend of the higher average values of oxytocin was observed in machine milking on day 5 of trial if compared with the values recorded during calf sucking, or the first milking (day 3), Fig. 1a, Tab. III. The mean oxytocin concentration during 7-minute milking (12.39 +/- 5.81 pg/ml) was significantly lower in the first-calvers on day 3 in comparison with the mean values recorded on day 5 (28.01 +/- 18.56 pg/ml; P < 0.001), or during sucking (18.32 +/- 7.15 pg/ml; P < 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)