NUTRITION

Feed and formulas for increased fertility
By Dr. Jim White

I’m confident that cows are grateful for my efforts to formulate feed for increased fertility. From a cow’s perspective, if you’re not bred, there is a very good chance of ending up dead.

The literature and practical experience are full of examples indicating that the nutritional status of beef cows will influence their fertility and reproductive efficiency. Pregnancy rates have been improved by altering any of the nutrient fractions of the diet: energy either as carbohydrate or fat, protein, mineral, vitamin. This is not intended to be an all encompassing list, but below I list some nutritional adjustments you can make to influence fertility and reproductive efficiency in cows.

Energy

The effects of feeding energy are pronounced. Feeding fat goes a long way to alleviate a milking cow’s negative energy balance. We have really good numbers on the influence of body condition score on the percentage of beef cows getting bred. Beef cows in good condition (BCS 5-6) will not respond with higher pregnancy rates if they get heavier. Cows in BCS 4 will significantly improve pregnancy rates if they gain a score. Cows in BCS 3 will have a much higher pregnancy rate if they can be bred at a BCS of 5-6 rather than 3. If you need to put weight onto cows, it will take a month and about 200 lbs. of Cattle Charge with forage to move the BCS one score.

Fat

On any number of occasions, feeding fat has improved reproductive performance. Improved energy status is a good explanation, and so are other explanations: Cows fed fat have higher levels of fat, cholesterol and progesterone, which tend to increase follicle size and embryo survivability. Feeding omega-3 fatty acids may inhibit the production or release of prostaglandin, which encourages embryo survivability. Prostaglandin will cause the CL to regress, and if it does, the survival of the embryo is guarded. We add Taltec to many feeds, and Super Cow products are formulated to contain both fat and omega-3 fatty acids.

Protein

Rumen-degradable protein that is eaten in excess of what can be used by the rumen microbial population will end up being turned into urea by the liver. Overfeeding soluble protein is more of a challenge with milk cows than with beef cows. The ability of a cow to utilize dietary nitrogen is directly influenced by the amount and type of rumen fermentable carbohydrate available. Soluble nitrogen helps fiber digestion, but you can use more soluble nitrogen as grain increases as a percent of the diet. However overfeeding soluble nitrogen and/or underfeeding fermentable carbohydrates is associated with reduced reproductive efficiency and MUN values in the high teens. This has been shown in studies where researchers fed the same amount of protein but varied the solubility—showing that cows perform best when certain specs are met, roughly a bit more than a third of the protein as rumen undegradable, and half of the degradable fraction as soluble. For this reason we have protein and nitrogen solubility specs on MFA ruminant feeds.

The question comes up “how does overfeeding soluble protein reduce reproductive efficiency?” There are several theories. One is the screwed-up-uterine-environment theory. That is, animals fed high levels of soluble nitrogen have been shown to have higher plasma urea levels and lower uterine pH, potassium, phosphorous and magnesium concentrations.

Then there is the energy-cost theory. That is, there is an energy cost associated with an animal converting ammonia into urea; the energy drain to convert the ammonia to urea may make the energy shortage even more pronounced. There is ongoing discussion about this theory. Overfeeding more soluble protein does not seem to make cows lose weight faster (it sure makes cows looser). However, feeding fat often reduces days to first service.

And there is the it-may-be-something-else theory: compromised liver function or reduced immune status have been suggested as possibilities.

Minerals

I love phosphorous—I mean other than white phosphorous. Over the last 20 years, I have seen more and more interest in not feeding phosphorous so aggressively as we did in the 1980s.

One common thought in the field is that feeding higher phosphorous improves reproductive performance. It certainly does when we started from the point of being phosphorous deficient. Beef cows should be getting at least 0.3 percent phosphorous in their diet, milking cows are going to need closer to 0.4 phosphorous. Research in the Midwest had shown that supplementing phosphorous to grazing cattle improves reproduction. Current work, using housed dairy cattle, indicates that adding higher than .4 percent phosphorous does not influence either animal production or reproduction.