Udder volume key to raised HGM yields
INCREASED milk yield from cows of high genetic merit, compared with those of low genetic merit, is largely a function of udder volume.
This reflects a greater mass of secretory tissue, not secretory efficiency. It also implies that attention should be paid to factors regulating udder development as well as function in future selection programmes, said researchers speaking at the British Society for Animal Sciences annual conference, at Scarborough.
Differences between 12 HGM and 12 LGM cows, obtained from the Edinburgh Blythbank and Langhill herds, were studied at the Hannah Research Institute, Ayr.
HGM cows represented the top 5% of the UK national herd while the LGM cows were close to the national average. The average balanced parity for both groups was 3.7 lactations. Measurements including milk yield, udder volume, body condition score, mammary enzymes, insulin, proloactin, thyroxine and cortisol hormone levels, were made over a period of two weeks, close to peak lactation.
HGM and LGM cows had similar body weights but daily milk yield at 37kg from HGM cows compared with 29kg for LGM cows. Udder volume was also about 1.3 times higher for the HGM cows and the calculated secretion efficiency, expressed as ml of milk per ml of udder tissue, was similar for both lines.
There was no difference in mammary enzyme levels, plasma metabolites or heart rate between the two lines but body condition scores were lower in LGM lines.
High yields from high genetic merit cows – its all about udder volume.