Watch high producers closely
It’s as plain as the numbers in your milking reports. Cows in early lactation are generally more profitable than cows later in lactation.
So it makes sense to manage cows to reduce calving interval and to have them spend more of their time in the earliest part of lactation. And it makes sense to focus on our reproductive programs and getting cows bred more quickly.
Of course, attention then steers toward nutrition’s impact on body condition score and cycling. Cows with lower body condition (2.5 or less) at breeding tend to be anovular (not ovulating). Cows with body condition at 3.0 or greater tend to ovulate.
However, research presented at last fall’s Penn State Dairy Nutrition Conference suggested that the difference in ovulation rates in the two groups isn’t as big you might anticipate. Anovulation rates in thinner cows were 35.5%, and heavier cows were around 20%.
So something more than body condition may be playing role in estrus cycling. And cows that are anovular tend to have reduced ovulation rates once positive energy balance is restored, even when hormonally induced.
When trying to establish the link between reproduction and nutrition, our focus has been on intake. The logic is that if we increase dry matter intake, we eliminate nutritional deficiencies and improve reproduction.
But, real-life experience and research now tells us that reproductive efficiency can be dramatically reduced by high feed consumption associated with high milk production. The likely culprit is a shorter estrus period.
Cows producing more than 80 pounds of milk per day have a shorter estrus (about 6 hours) compared to lower-producing cows (about 10 hours). That shorter estrus is likely the result of a reduced amount of the hormone estradiol.
• Reducing calving intervals and getting cows bred more quickly pays off.
• Nutritional deficiencies aren’t the problem in high producers.
• Manage these cows’ reproduction cycles and heat detection separately.
Nutrition has little to do with it
High-producing cows eat lots of feed to meet milk-producing energy demands. High feed consumption increases blood flowing to the digestive tract to pick up those nutrients.
All that blood also has to flow through the liver — the animal’s metabolic powerhouse. It rids the body of many compounds, including hormones like progesterone and estrogen.
Lower estrogen and progesterone decrease ovulatory cycles and their duration. So nutrient deficiencies probably aren’t causing anestrous. And adding “foo-foo dust” and “zippity-do-dah by-pass nutrient of the month” probably won’t improve reproduction.
What you can do
Managing high-producing, high-intake cows differently can help improve reproductive efficiency. How so?
• Group cows according to stage of lactation.
• Maximize cow comfort. It’ll help you spot cows in heat.
• Increase the number of times you observe heats. For example, watching for heats four times a day will detect about 90% of those in estrus that are producing around 70 pounds per day. But it’ll detect only about 50% of those producing more than 100 pounds. Detection rates get even worse if it’s done only once or twice a day.
• Heat detection aids such as tail chalk help find cows showing heat when people aren’t present. This can be critical, because high-producing cows are only in heat for about four hours per day.
• Minimize the change in body condition from late lactation to dry-off to early lactation. This will reduce the duration and severity of negative energy balance, and cows will begin cycling.
• Feeding good-quality feed so your cows have access to it all day and night will help minimize body condition changes. High-forage diets tend to reduce body condition fluctuations.
If you know high producers are harder to get bred because of shorter estrus, invest in heat detection time and/or heat detection aids. It’ll pay back better than nutritional supplements.
Carson and husband Steve partner in Harkdale Farms of Newbury, Vt. She’s also a professor at Vermont Technical College.
This article published in the March, 2010 edition of AMERICAN AGRICULTURIST.