Nutrition in Dairy Reproduction
Published on Fri, 04/24/2009 - 12:22pm
A lot goes into achieving a successful calving rate in your herd-including, of course, what goes into your cows. University of Minnesota Extension dairy nutritionist Noah Litherland says one of the biggest challenges in dairying is getting cows back into positive energy balance after calving; he says strong feeding strategies for both dry and fresh cows are part of the solution, and it's important to ensure there's adequate macro- and micro-minerals in the diet.
"Providing adequate selenium will potentially reduce retained placentas," he says, "which will lower the incidence of metritis. So getting the uterus involuted after calving, maintaining health, getting cows back in positive energy balance are all important things that a good, sound nutrition program can do to improve reproductive efficiency overall." A sound mineral program is also important for the prevention of milk fever, or hypocalcemia.
But while energy is important, you can't overdo it. "Minimizing overconditioning in cows, or overfattening in cows, during the late lactation and dry period will tend to give them a little better chance for success after they calve," says Litherland. "A little bit of fat to mobilize off their backs to increase milk production is great; excessive amounts of fat tend to increase the risk for ketosis, increase the risk for fatty liver-all are associated with energy balance of the cow, which eventually is tied with reproductive function. Long levels of negative energy balance tend to reduce normal cyclic patterns, and so we tend to get longer days for service, longer days to get conception. So, it does tend to decrease reproductive efficiency."
But on the whole, undernourishment is more of a threat to conception than obesity. Litherland says producers could consider delaying service of an underconditioned cow on a case-by-case basis. "It might be important to look at what your breeding strategy is," he says. "Are you using sexed semen? Are we trying to flush embryos? If that's the case then, yes, it would probably make sense to delay.” But if the cow is already in heat and in reasonably good health, he says, the best strategy is to get her bred as soon as possible. While some producers breed on the first estrus following calving, others wait until the second; if they’re using ovulation synchronization hormones, they can breed a large number of animals at once and improve the overall efficiency of their reproductive program.
Conception problems can have many causes, but there are ways to address the nutritional aspect. Adding fat to the diet can be helpful, says Litherland-"Some fatty acids have been shown to increase reproductive efficiency, although results are not always consistent.
Evaluate the level of protein in the diet; sometimes excessive amounts of dietary nitrogen can reduce overall reproductive efficiency, so that might be something to kind of take a look at."
Litherland's colleague, University of Minnesota ruminant nutritional physiology professor Brian Crooker, notes the presence of a specific type of fat in the diet can make a difference; researchers presume polyunsaturated fatty acids have some involvement in reproductive performance, and are working on ways to enhance their presence in the animal's system. "Those fatty acids can be hydrogenated in the rumen by microorganisms that live there," he says. Hydrogenation-altering the fat's chemistry by attaching hydrogen ions to the double bonds-alters what the fat can do, so there are studies into ways to protect the fatty acids in the rumen and allow them to pass through to the lower gut, where they are absorbed into the bloodstream. "There are a variety of ways to try and protect those fatty acids," Crooker says, "either encapsulating them in some compound that the organisms can't get through, or just making them unavailable to the microorganisms." The producers could simply increase the percentage of polyunsaturated fats in the diet, but that can get to be expensive, he says: "If you're trying to isolate or provide an individual purified fatty acid, usually when you try to do that, you try to protect it in some manner."
Crooker views the reproductive effects of body condition based both on where the cow is, and where she's going. He explains, "You typically score cows on a five-point scale, 1 being very thin, emaciated, and 5 being obese. Score them on quarter points, so a cow that's 3.25 is in pretty good shape in early lactation, but if a cow is at 2 or less-if she started out at 3.25 and is dropping down to 2, and she hasn't hit bottom yet-then she could be in trouble." On the other hand, he says, if her condition fell to a 2 but is recovering, "then she might start to get ready again. So it's really a dynamic change, whether the cow is stable or changing."
If the cows aren't performing well on a farm that's doing a good job of managing the diet formulation, Crooker says the ration composition usually isn't the problem; instead, it's often the cow's ability to gain access to the diet. She may have a metabolic problem that's dulling her appetite, or bad feet or legs that discourage her from getting up and going to the feed bunk. "What you're really trying to do in those high producing cows," he says, "is convince them to eat another pound of food, convince them to consume those nutrients that they need in order to produce the milk that they're producing. If they don't consume enough of the diet, then they'll have to take it from their bodies' stores, just like humans-if you decrease your intake, you'll start losing weight." Litherland adds that the cow's environment can be a factor. He says, "Happy, comfortable cows that are clean, in a stress-free environment, really go a long way toward marrying up to a better nutrition program to improve overall farm efficiency, but those factors will all impact reproductive efficiency as well." He calls the six weeks surrounding calving "a very tumultuous and stressful time for a lot of cows," and says a successful all cow management program begings with helping her navigate through that period.
"Our involuntary cull rates in our US dairy herd overall are 20-30%," he says, "which in a lot of ways in unacceptable. If we can improve the overall health of the animals, avoid metabolic disorders such as ketosis, fatty liver, milk fever, and minimize metritis and mastitis through that early lactation period, I think we can do a lot better job, and be more efficient managing our cows reproductively." Hypocalcemia, in particular, causes lower smooth muscle contractions, which may reduce the ability to expel the placenta normally; in addition to increasing the risk of metritis and the resulting reduction of reproductive efficiency, the affliction also reduces the ability of the teat sphincter muscle to contract. That, Litherland says, "increases the risk for mastitis, which is also associated with increased culling and reduced efficiency on the farm."
Whether you should cull a cow that's a problem conceiver, he says, depends on the bottom line. "We certainly have folks breeding cows five, six times to get a conception," Litherland says. "The farm's overall objective, the level of milk production, the quality of genetics of the cow...all have to kind of factor in as terms of really understanding when that animal should be culled. It comes down to the fact that the producer needs to know the dollars that they're spending in terms of maintenance of the animal, and the costs to break even."