Lift HGM cows DM post-calving
Lift HGM cows DM post-calving
By Hannah Velten
FEEDING to increase cow body condition post-calving can lift conception rates in high genetic merit (HGM) cows which experience energy deficiency in early lactation.
Speaking at an MDC Focus Centre meeting in Staffs, Chris Reynolds said his research at the University of Reading to measure energy metabolism in HGM Holstein-Friesians, showed body energy was lost until at least week 14 of lactation.
"Trial Holsteins were milked three times a day and yielded over 10,500 litres/lactation. With maximum feed intake of 25-26kg DM a day of conserved feeds at 10.82 MJ/kg DM, they were found to require 281MJ of metabolisable energy a day. To support milk production, about 1kg of body tissue was metabolised a day, which led to a loss of body condition, even though body weight increased – due to gut fill – after lactation week five," said Dr Reynolds.
Metabolic demands on the high yielders reduced their fertility by altering ovarian function, he said.
Milk progesterone testing detected the cows ovarian cycles and progesterone levels took longer to rise in the HGM cows compared with average cows – 23 versus 15 days – and continuing cycles tended to be dysfunctional.
Stopping energy loss as soon as possible after calving was crucial to restoring normal ovarian functioning, said Dr Reynolds. "Cow condition score, not their liveweight, will indicate energy balance and it should not fall below two."
Although Holsteins can eat and drink up to 25% of their body weight daily, the diet must be high in dietary energy.
Maximising DM intakes and hence ME could be achieved by using a mixture of forages where possible and/or drier diets, said Dr Reynolds. Effective physical fibre, such as small amounts of chopped straw or hay, could also help promote rumen function and intake.
Inclusion of fats in a mixed ration was another strategy to increase ME, but it should not exceed 7-8% of the diet, warned Dr Reynolds. "Although effects of fat on fertility are still being researched, higher cholesterol levels may elevate progesterone and specific fatty acids may improve ovary or uterine function. But excessive feeding of cheap sources of fat may exacerbate infertility."
Increased fat feeding may stimulate the lactation response and make negative energy balance worse, he warned. "Excessive protein in the ration must also be avoided. Even though protein will increase intake, it must be balanced with fermentable metabolisable energy so excess protein is not absorbed as ammonia," said Dr Reynolds.
High levels of milk urea may result in poorer fertility, but may also be an indicator of excessive energy loss from the body. *
FEED AND FERTILITY
• Body energy losses in HGM cows.
• Leading to infertility.
• Increase DM intakes and ME.
Metabolic demands on HGM cows reduces their fertility by altering ovarian function, says Chris Reynolds.