Wednesday, November 22, 2017

Cow's Body Condition Score will impact calf health and pregnancy rates next year

Earlier than normal snowfall this year may necessitate feeding cows
earlier than normal.  Body condition score at calving impacts calf
vigor and health and cow breed back next year.  Photo by Kari Lewis.
Kari Lewis, MSU Extension – Glacier County

                Recently as I looked through our cows, I was concerned about some of the cows’ body condition scores.  There’s multiple factors that have had a role in our herd’s body condition being lower than I would like to see.  First, this summer’s drought resulted in less forage than normal, then the early October snowstorm hit the cows hard as well.  In addition, our weaning date was later than it should have been, which meant the cows were also lactating longer into the fall, using additional nutrients to support their calf at side.  Not surprisingly, it is our youngest cows who are the thinnest, as they’ve also been trying to grow in addition to supporting their calf and developing fetus. 
                As cows receive nutrition, they first use it for maintenance, then allocate the remaining nutrients to support fetal development, lactation, growth, and lastly, rebreeding.  Thus, if a cow is short on nutrition, the first thing to be impacted is her ability to rebreed.  Therefore, it’s critical that we provide adequate nutrition now to ensure cows are in an acceptable body condition to rebreed next summer. 
A body condition score (BCS) describes the relative fatness or body condition of a cow on a scale of 1 to 9.  A score of 1 means the cow is extremely thin, and a score of 9 indicates a very obese cow.  Each body condition score translates to approximately 70 pounds, so to increase a BCS 4 cow (on December 1) to a BCS 6 cow (by March 1) would require that cow to gain 1.6 pounds per day, not including the increasing weight of her fetus. 
                Why is body condition so critical?  Simply, thin cows take longer to rebreed, produce less colostrum, and give birth to less vigorous calves.  Those calves that are born weak at birth take longer to nurse, have lower immunoglobin levels which lessens their ability to overcome disease, and are ultimately less likely to survive. 
A cow’s BCS at calving is a large indicator of how soon she will rebreed following calving.  A cow that calves in a BCS 5 or 6 averages 55 days following calving until her first heat, while cows that calve in a BCS 3 or 4 average an 80-day post-partum interval.  Knowing that we want those cows to have one or two heat cycles prior to when they are bred, it’s easy to see why thin cows fall out of the herd.  Data from Spitzer et al., 1995 showed that first calf heifers that calved in a BCS 4 had a 56% pregnancy rate after a 60-day breeding season, whereas those heifers that were in a BCS 5 at calving had an 80% pregnancy rate, and there was a 96% pregnancy rate in the heifers that calved at a BCS 6. 
                The period after weaning (when nutrient requirements are decreased) and before the third trimester begins (when nutrient requirements increase again) is the most economical time to add body condition.  By providing adequate nutrition, a windbreak, straw during cold weather, and access to clean, fresh water, we can add condition to the cowherd to meet our breed back goals for next year.  

Here at the MSU Extension office in Glacier county, we can assist you in formulating a ration for your cowherd.  We have two hay probes that can be checked out to sample your hay for a nutrient analysis, and can use ration balancing software to formulate a ration that will meet your cows’ protein and energy needs.  Please call (406) – 873-2239 or e-mail with questions, I’m happy to help!              

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