Feeding The Fetus

It's been said you can't starve a profit out of a cow. Based on new and ongoing research at the University of Nebraska, you can't starve a profit out of the calves incubating inside those cows, either

It's been said you can't starve a profit out of a cow. Based on new and ongoing research at the University of Nebraska, you can't starve a profit out of the calves incubating inside those cows, either.

“Supplementing cows with protein while grazing dormant Sandhills winter range during late gestation not only affects the nutritional plane of the cow, but has lasting effects on their heifer calves' weight and reproductive performance,” explains Rick Funston, a University of Nebraska (UN) beef cattle reproductive physiologist.

Funston is referring to a three-year study evaluating the effect of dam nutrition on the growth and reproduction of heifer calves. It was conducted at the UN Gudmundsen Sandhills Laboratory near Whitman, NE. How about this: 88% of heifer calves from cows supplemented with protein during the last trimester achieved first-service pregnancy, compared to 45% of heifers out of cows receiving no supplementation.

In addition, heifers from supplemented cows had a higher overall pregnancy rate (94% vs. 73%) and calved eight days earlier and had fewer calving problems (69% unassisted births vs. 38%), though calf birth weights were about the same. Weaning weights and prebreeding weights were higher for calves out of supplemented cows (Table 1). Basically, no difference was seen when evaluating subsequent early lactation nutrition — one group grazing sub-irrigated meadow and another receiving hay.

This is the first beef cattle research to demonstrate the startling impact late-gestation nutrition has on the performance and subsequent reproductive efficiency of heifer calves.

For perspective, the supplemented group received the equivalent of 1 lb. of protein supplement (42% crude protein)/head/day from Dec. 1 to Feb. 28 (calving March 1 to April 30).

In an associated three-year study — examining the effects of prepartum and postpartum nutrition on reproduction in spring-calving cows, and calf feedlot performance — cows receiving protein supplementation weaned 5-9% more calves than cows not receiving supplementation.

“It doesn't appear to be a passive immunity challenge. Though we don't know all the metabolic signals involved, it seems to be more an effect of neonatal programming,” Funston explains.

He emphasizes that these studies were built upon an earlier one conducted by fellow researchers Aaron Stalker and Don Adams, the latter the director of UN's West Central Research and Extension Center in North Platte. Their research examined the impact of early weaning and protein supplementation to maintain Body Condition Score (BCS) and enable year-round grazing.

That study found a dramatic increase in carcass weights (as much as 60 lbs.) from steers born to cows supplemented in late gestation, compared to steers from unsupplemented cows. Surprisingly, though, neither early weaning nor supplementation impacted a cow's reproductive performance as long as she was on a positive plane of nutrition after calving. Researchers concluded that fetuses were drawing on maternal nutrition reserves, be it from supplementation or from higher stored reserves preserved by early weaning heading into calving.

“It's body-condition dependent,” says Funston. In other words, the key seems to be achieving a positive plane of nutrition during late gestation, or maintaining adequate BCS, however it's accomplished.

For instance, looking across these various studies, Funston says, “You don't see or expect to see as much impact in the calves from early-weaned cows.” In spring-calving herds, those cattle have more time to build and pad nutritional reserves.

Funston also points out that the cows in the study were no less than a BCS 4 when the last trimester began; the goal was BCS 5 at calving. So there's no telling if the same improvements are possible with thinner cows before and during late gestation.

“We generally focus on management that impacts the cow, and manage herds for least cost,” Funston says. “But this research shows our management may also be altering the profitability of the unborn calves in those cows.”

Table 1. Effects of dam protein supplementation on heifer reproductive and calving performance
Protein1 Supplement No Supplement
Birth weight (lbs.) 79 77
Weaning weight (lbs.) 467 456
Adj. 205-day weight (lbs.) 498 481
Prebreeding weight (lbs.) 608 586
Subsequent effect on reproductive and calving performance of these heifers
Cycling at beginning of breeding season (%) 47 50
First-service pregnancy (%) 88 45
Overall pregnancy (%) 94 73
Calf birth weight (lbs.) 75 74
Unassisted births (%) 69 38
142% CP supplement fed equivalent to 1 lb./head/day Dec. 1 to Feb. 28.
Source: University of Nebraska