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NUTRITION – for Jan. 10, 2011

Now that we have gotten through another holiday season and are looking forward to a year that promises strong demand and prices, it is time to think about basic biology, particularly reproductive biology of the cow. While this subject may not make your top-10 list, it is important to refresh ourselves on the role nutrition plays in successful calving and breeding programs. This is particularly of value for those of you calving in the next six to 10 weeks, but should be on your radar even if you are calving later in the spring.

As a successful rancher you have learned (sometimes the hard way) that how you manage your cows influences breeding and calving success, milking ability as well as weaning weights. All critical factors influencing herd productivity and profitability! Proper management starts with an understanding of the reproductive biology of the cow. In any given year, a typical cow is pregnant for nine months and a bit! Calving is critical, not only because of the arrival of the calf, but also because the cow starts milking, a process, which continues through weaning. Following calving, the cow typically does not show heat for a period of 20 to 40 days. This anestrous is due to stress placed on the cow from pregnancy, calving and milk production. The important point if we do the math is that to keep her on a yearly calving interval, you have 40 to 60 days or two to three heat cycles to get her bred. It is also important to know that this period of anestrous can last considerably longer than 40 days (i. e. 60 days or longer). In such cases, the reason can often be traced back to a poor nutrition program. With these cows, it is almost impossible to keep them on a yearly calving interval.

The key to proper breeding management is an understanding that there are two critical periods in the cow’s annual reproductive calendar. These include the last 60 days of pregnancy and the time frame from the onset of milk production through breeding. The last 60 days of pregnancy is the time where the growing fetus begins to place a significant demand on the dam for nutrients. Consider for example a 1,300-pound cow in the last month of pregnancy. This cow should be gaining approximately a pound a day and according to Alberta Agriculture’s Cowbytes program, requires 16.0 pounds of TDN (energy), 2.0 pounds of crude protein, an ounce of calcium and half an ounce of phosphorus daily, assuming normal winter conditions. She also needs to be on an appropriate trace mineral and vitamin (A, D, E) program as we discussed last month. These levels of energy and protein are 25 to 33 per cent higher than those of this same cow in mid pregnancy. The onset of milk production following calving will further increase the need for these essential nutrients.

Failure to meet the cow’s feed requirements during these periods will have dramatic effects on body condition and reproductive performance. Consider these facts on cows that go into calving in poor condition or lose excessive weight post-calving:

They will have a longer postpartum period where they do not show heat and can have lower conception rates and as a consequence they are more likely to be open in the fall. Milk production suffers, putting the health and growth of the calf at risk.

Those that do rebreed do so later in the season and subsequently wean lighter calves the following year.

In essence, if we fail to meet the nutritional needs of our cows during the last 60 days of pregnancy and following calving, we can expect delayed rebreeding, poor conception rates and an increased percentage of open cows. Furthermore, our next calf crop can suffer higher death losses, longer calving intervals and reduced weaning weights.

As managers, we have the opportunity to develop feeding and management programs that optimize breeding performance, milk production and calf growth. A sound nutrition program is based on knowledge of the animal’s nutrient needs, and on feed quality and quantity. Knowing how much energy to feed is a combination of using established requirements and common sense, particularly when the weather turns on us. Feeding good quality hay or additional grain or other energy sources such as fortified grain screenings can help get your cows through periods of severe cold. Forage quality is best determined by a feed analysis, particularly in years like this where many of us are forced to feed hay that has been put up under less-than-ideal conditions. A feed analysis will indicate the energy and protein content of your forage and give you a sound basis for developing your pre-and post-calving feeding programs.

As you move towards this year’s calving and breeding seasons, keep in mind that the goal is to wean a healthy calf from each cow exposed on a yearly basis. Your ability to achieve this goal begins with a sound nutrition program!

[email protected]

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JohnMcKinnon isabeefcattle nutritionistat theUniversityof Saskatchewan

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John McKinnon

John McKinnon is a Professor Emeritus at the University of Saskatchewan and a consulting nutritionist who can be reached at [email protected].

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