UNL talks principles for improving conception rates with estrus synchronization

Published on March 21, 2020

“Currently there is a lot of buzz over efficiency, and efficiency is obviously important because feed is the biggest cost for any part of the production cycle,” states Dr. Rick Funston, beef cattle reproductive physiologist at the West Central Research and Extension Center at the University of Nebraska-Lincoln (UNL). “But I would argue reproduction is also critical to the efficiency of a beef system.” 

In a webinar hosted by the University of Nebraska, Funston discusses the importance of estrus synchronization in beef cattle production systems.

Advantages of synchronization

“There are many advantages of synchronization including increasing pregnancy rates by allowing more opportunities to conceive, and therefore, reducing replacement rates as well as earlier average conception and calving dates, and therefore, heavier calves at weaning,” Funston says. 

            A study conducted by Funston and colleagues at the Gudmundsen Sandhills Laboratory looked at how birth date affected several economically important traits in steers and breeding females.

            “In the steers, we saw those born earlier had greater weaning weights, carcass weights, marbling scores, higher average choice and higher carcass value,” states Funston.

             “In the heifer calves, those born earlier were heavier at weaning, heavier at pre-breeding and exhibited more cycling prior to breeding,” he adds. “They also have greater pregnancy rates, wean a heavier calf and breed back sooner.” 

            Funston notes different research done by a colleague found it takes the profit from two early-calving cows to cover the loss from one late calver. He also found a cow calving in the first 21-day calving interval for her entire eight or nine year life will produce the weaning weight equivalent to two additional calves in her lifetime compared to one that starts late and stays late. 

Synchronization products

When it comes to products producers can use for synchronization, Funston has some suggestions. 

“Do not use ECP or compounded estrogens because they are illegal and not more effective than anything we have that is legal,” Funston says. “Oftentimes we think things we don’t have access to are going to be better, but this isn’t the case.”

Funston notes there are plenty of other effective options to choose from including prostaglandins like Lutalyse, Estrumate and SYNCHSURE, progestins in the form of melengestrol acetate (MGA) or controlled internal drug release (CIDR)  and gonadotropin-releasing hormone (GnRH) products used concurrently with progestins. 

When it comes to pre-breeding vaccination recommendations, Funston says replacement heifers should be vaccinated before and at weaning, both heifers and cows should be vaccinated 30 days before breeding and animals that have not been previously vaccinated should not receive pre-breeding vaccinations. 

“Animals are safe to transport either right after receiving vaccinations or around 45 days afterward,” Funston says. 

MGA versus CIDR

            For heifers, Funston recommends using a long-term progestin protocol synchronization technique such as MGA prostaglandin or a 14-day CIDR. 

            “We did a large study comparing these two techniques on 1,400 heifers and they were spot-on identical,” states Funston. 

            “The key with MGA is they have to consume it every day. Also, there is no compelling data showing there is anything better than the seven-day CIDR for cows who have already had a calf,” he adds. 

            Funston notes a study done by UNL showed no advantage in estrous detection over timed breeding.

He also reminds producers synchronization can be used effectively with natural service. 

Fertilization rate

“Fertilization rate in most mammals is incredibly high,” states Funston. “It is estimated to be upwards of 90 percent. However, we lose 30 percent of the embryos before day 30.”

“This is disheartening because of the amount of research that has been done to understand this and the huge economic implications it has on the industry,” he adds.

He notes there are four main categories of factors affecting embryonic loss which include genetic factors such as expression of lethal genes, abnormal chromosomal numbers and inbreeding, environmental factors such as heat stress, transport and handling/chute work, nutritional factors such as body weight and body condition score at breeding, excess protein or toxins and miscellaneous factors such as low progesterone production, age of dam, semen quality and infectious agents. 

Sire selection

Funston says sire selection determines more than 85 percent of the total improvement made in a herd. 

“If we are going to make genetic change in a herd we are going to do it through sire selection, not through any one female,” he explains. 

Funston also explains some key questions producers need to ask before purchasing semen are if they are keeping replacement heifers and when they sell their calves. 

He also reminds producers to be proactive, understand expected progeny differences (EPD) and selection indexes, what they are looking for and not to waiver at the sale barn. 

Anestrus and nutrition

Funston states there are several types of anestrus cattle may be in.

These include nutritional anestrus, pre-pubertal anestrus, lactational anestrus and pathological anestrus such as reproductive problems like pyometra, metritis and endocrine dysfunction.

Funston explains anestrus can be identified through age and weight in heifers, days postpartum and body condition. 

“Nutritional anestrus is probably the biggest issue as they have a lack of adequate energy to provide for reproductive systems,” says Funston. 

“Balanced nutrition is key to optimizing production,” he adds. “Cattle need the right balance of protein, energy, minerals, vitamins and water.”

“Energy from a nutrient standpoint is the most important, but oftentimes we need to supplement protein when feeding low-quality forage,” Funston says. 

Factors affecting production

“We talk about three things in genetic selection with the biggest impact on production,” says Funston. 

“The first is dystocia, which is why we breed for calving ease. There is a 16 percent advantage in conception rate to cows without dystocia. These animals don’t have calving difficulty and breed back sooner,” he explains. 

“The second is milk. When we have cows producing a lot of milk in a limited resource environment, something has to give and this will most likely be production,” Funston adds. “We need to keep a balance between productivity, resource availability and cost. Selecting for increased milk production will not be profitable in all systems.”

“The third is mature size,” he continues. “As our cattle get bigger, we need more nutrient resources unless we are willing to sacrifice reproduction. The most desirable cows to have on an operation are those that excel early in growth but mature at a moderate weight.”

Hannah Bugas is the assistant editor for the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.