The Cow-Calf Manager

Livestock Update, April 2003

John B. Hall, Extension Animal Scientist, Beef, VA Tech

Rough Winter Could Spell Breeding Season Trouble

The first warm days of spring and greening grass have most producers looking forward to the first good year in 3 or 4 years. However, in my travels around the state this winter, I noticed that cows are in the worst body condition and nutritional status that I have seen in the 6 years I've been in Virginia. The hard winter and short hay supplies resulted in cows losing too much weight this winter. Thin cows will not re-breed successfully this spring resulting in too many open cows this fall. Many herds in Virginia are in danger of a disastrous breeding season.

Poor body condition puts breaks on reproductive system

Cows in poor body condition will be delayed in the resumption of estrous cycles after calving. The beef cow's body has built in "sensors" that relay information about cow body condition and nutrient supply to the centers of the cow's brain that control reproduction. Although all the sensors and messengers are not fully understood, research from several states indicates that energy availability is the critical factor. Energy availability includes cow body fat stores as well as energy in the diet.

Cows in low body condition score (< 5) may be 90 to 120 days post-calving before they have their first heat. Cows in extremely poor condition (BCS ¾ 3) may not resume estrous cycles until calves are weaned or they gain 100 to 150 lbs. As a result of poor body condition at calving or breeding, pregnancy rates for cows with BCS < 5 will be lower than cows in good condition (Table 1). All beef producers should body condition score their cows immediately. For information on body condition scoring cows see VCE Publication 400-795. Producers can use the herd's cow body condition scores to plan management strategies.

Table 1. Effect of Body Condition Score at Calving on Cumulative Pregnancy Rates

		Day of the Breeding Season
	BCS	20 d	40 d	60 d
Mature Cows (Richards et al., 1986)		Cumulative % Pregnant
	¾ 4	41	67	84
	„ 5	51	79	91
First Calf heifers (Spitzer et al., 1995)		Cumulative % Pregnant
	4	27	43	56
	5	35	65	80
	6	47	90	96

Increased nutrition will help, but April grass not enough
Cows that are fed to gain weight between calving and breeding will breed earlier and have higher pregnancy rates than thin cows that remain thin. Increased energy intake will cause thin cows to gain weight and cycle earlier than cows that do not gain weight. (Figure 1.). Feeding high energy diets will increase pregnancy rates by 20%. However, pregnancy rates will not be as great in thin cows gaining weight as cows that calved in good body condition.

Early spring grass is high in energy and protein, but low in dry matter and fiber. As a result, it is difficult for cows to eat enough grass to meet their nutrient needs especially if the grass is short. Also, the rate of passage (how fast feed moves through the digestive system) is very rapid, so nutrients are poorly absorbed.

Thin lactating cows need high energy supplements from calving through the breeding season. If cows are eating hay as the primary forage then recommended energy supplements include corn gluten, whole shelled corn, rolled barley, or soy hulls. For cows grazing early spring grass, supplements include cracked corn, rolled barely, or a 50:50 mix of cracked corn and corn gluten. Thin cows will need up to 1% of their body weight in supplement. This would be 12 lbs of supplement for a 1200 lb. cow. In addition, cows grazing spring grass need a source of roughage to slow the rate of passage, so supplements will be better absorbed. Roughage sources include low quality hay, straw, poultry litter, peanut hulls, or cottonseed hulls.

Early weaning may be an option
For extremely thin cows or 1st calf heifers, early weaning of calves may be the best management choice to ensure a high pregnancy rate. Calves can be early weaned as young as 90 days. Once the calves are weaned, cows gain weight rapidly and resume estrous cycles with in 2 to 3 weeks. Contact you county extension office or see http://www.ext.vt.edu/news/periodicals/livestock/aps-99_07/aps-0082.html for examples of early weaning diets.

Pay now or pay later
The options discussed are not cheap and require additional labor. After high feed costs for most herds this winter, many producers are reluctant to spend money on supplements as the grass greens. However, failure to employ management strategies to increase energy intake and body condition between calving and breeding will result in too many open cows this fall and a low calf crop next spring.

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