The objective of this experiment was to investigate the effect of milking frequency and nutritional level on some aspects of animal health. Holstein-Friesian cows (n = 60) were assigned post calving to a factorial arrangement of treatments; twice a day (TAD) milking on a high or low nutritional level; once a day (OAD) milking on a high or low nutritional level. Milking characteristics were recorded daily. Blood samples to evaluate changes in the composition of the blood cells, milk leakage, udder tension and locomotory ability were measured on four occasions. Teat-ends were classified for hyperkeratosis (HK) monthly post partum. TAD had longer daily milking times (P < 0.001) compared with OAD cows. There was no effect of milking frequency or nutritional level on morning milking time, time to milk letdown or peak milk flow rate (P>0.05). High nutritional level cows had higher average flow-rates (P < 0.05) than low nutritional level cows. Neither milking frequency nor nutritional level affected HK (P>0.05). However, HK values were positively correlated with daily milking time for OAD cows for 6 months of lactation (P < 0.05). This correlation was significant (P < 0.01) for cows milked OAD on high nutrition during the peak lactation period. OAD cows had higher levels of milk leakage compared with TAD cows during the month of May (P < 0.01). Cows on high nutrition milked OAD showed higher udder firmness scores than cows milked once or twice daily at the low nutrition level in June and July (P < 0.05). OAD cows had higher locomotion scores compared with TAD cows (P < 0.001). Locomotion and udder firmness scores were significantly correlated for OAD in June (P < 0.05). OAD cows had lower blood lymphocyte counts, numerically higher counts of neutrophil and a higher monocyte count at peak lactation compared with TAD cows suggesting that OAD cows had altered immune responses. The increase in milk leakage, higher udder firmness and locomotion scores in conjunction with changes in blood cells, suggests that OAD milking may have caused some discomfort to the cows during peak lactation. A reduction in the concentrate input to OAD cows during this period could ameliorate this problem.

Unsatisfactory milking conditions, including high milking vacuum, ineffective pulsation, heavy clusters, unsuitable liners, poor teat preparation and over-milking, are known to create poor, but undefined, teat conditions and pose a risk to an increased probability of intramammary infection (IDF, 1994). It has been shown that poor teat condition, seen as discolouration, abnormal firmness or thickened rings of tissue distally, after cluster removal may be common in a variety of commercial milking operations (Hillerton et al. 2000). That field study was observational and teat conditions were influenced by a number of variables. A small experimental study has been undertaken to develop an experimental model, under controlled milking conditions, to allow investigation of potential causes of teat trauma. Over-milking was suggested as highly important in the field observations and so has been examined in this study.

Previous research has shown that piglets using the sow's more anterior teats tend to have greater average weight gains, but this difference is often slight in the first lactation and increases in subsequent lactations. In this study, 27 sows were used to determine whether this difference develops because of the piglets' preferential use of the anterior teats during the first lactation. In their first lactation, 14 sows had their anterior teats (pairs 1 to 3) and 13 sows had their posterior teats (pairs 4 to 7) covered so that the piglets could use only one end of the udder. In the second lactation, all the teats were left uncovered and the sucking positions and weight gains of the piglets were studied. Piglets in the second lactation showed the usual preference for anterior teats regardless of which teats had been used in the first lactation. Where the anterior teats had been covered in the first lactation, there was no difference in weight gain between anterior- and posterior-sucking piglets in the 1st week of the second lactation, but a degree of anterior superiority had developed by the 3rd week (P < 0·01). Where posterior teats had been covered in the first lactation, piglets using anterior teats showed substantially greater weight gains than those using posterior teats throughout the first 3 weeks of the second lactation (P < 0·001). Thus, non-use of a teat in the first lactation tended to reduce its productivity, at least in the early part of the next lactation. We conclude that previous non-use of posterior teats can contribute to their tendency for lower productivity, but the effect does not explain completely the greater piglet weight gains usually associated with using the anterior teats.