Summer calving can be super!


Source: Ministry of Agriculture, Food and Rural Affairs

The choice of a season for calving is a fundamental decision made by cow-calf producers. Some surprising research results indicate that there may be some big advantages to breaking with the tradition of calving prior to the pasture season.

The majority of Ontario cow herds calve in late winter /early spring, with the two most popular months being March and April. Reasons given for this choice of season (rather than later in the year) include heavier calves for fall sales, making the best use of pasture and getting calving over prior to cropping activities.

But those who calve during this time of year are all too familiar with the down side … frequent night checks through the snow to ensure live calves during cold snaps and warming up chilled calves with various devices. April brings warmer temperatures and … mud. Wet conditions and manure build-up is a recipe for a calf scours outbreak, even though you used lots of straw.

Backing calving up into February may help to minimize scours, but at the price of increased cold weather stress.

Building more elaborate facilities for calving helps, but beef cows don’t have strong backs when it comes to supporting a debt load . Overall, its hard not to end up with a management intensive system and an associated case of “calving burn out” for herd managers.

For many operations, the high level of vigilance and management required during calving season is a primary limiting factor of herd size. And with profit per cow usually pretty low, it sure would be nice to have a few more head around to dilute overhead and increase total revenue!

One alternative which may address some of these problems is to calve later in the year, when cows are on grass. This would mimic the reproductive pattern of wild ruminants like deer, who tend to get along with little human intervention. Cold weather concerns would be gone. And with cattle spread out over a large area, it stands to reason that the disease challenge to calves from manure borne microbes would be reduced.

These were some of the ideas behind a long term research project at the New Liskeard Agricultural Research Station. Since 1992, the Cow-calf Production Systems Project has been evaluating calf production based on summer pasture calving, compared with a traditional winter calving system. The project was started when the facility was part of the Ontario Ag Ministry’s College system. It continued as the University of Guelph took over the reins of all of the Aggie Colleges.

The rationale for summer calving included potential cost savings for labour, bedding and capital facilities, as well as lower incidence of calfhood disease. If these could be realized and combined with a lower level of calving season stress on managers, financial benefits could be substantial. They would include both a higher margin per cow, and a greater number of cows possible per farm.

Concerns which were raised included the potential for higher death losses of cows and calves from dystocia, difficulty in locating newborns for processing, and less efficient disease detection and treatment.

In 1992, the 100 large frame crossbred cows in the research herd at New Liskeard were divided into two seasonal groups. During each year, the same sires were used in both seasons. Predominant sire breeds were Charolais, Limousin and Angus. This report covers 5 years of the project, representing a total of 558 calvings.

The traditional group was bred to calve from mid February to early April. They were wintered in naturally ventilated barns with access to outside. These cows were calved out in small pens in an enclosed, non-heated barn, with cows and calves returning to an open front barn within 2 days. This group went to grass in late May/early June, with calves being weaned in the fall.

Cows in the alternative system were calved during June- August in 20-25 acre pastures. These calves remained on the cows until weaning in January. After the pasture season, the group was housed in an open front barn and fed stored forage, with calves receiving a limited amount of grain based creep feed.

Here’s what we found …

Average birth weight was 6.0 lbs lower with the Summer calving group (see Table 1). This effect was consistent across years and breeds of sires. At first glance, this may not seem like a large difference. But think in terms of bull selection … calving in summer had a net effect similar to reducing a sire’s birth weight EPD by 6.0 lbs. This would allow managers much greater flexibility in choosing bulls.

There may be several factors contributing to the lower birth weights seen in summer. One may be an effect of temperature during gestation on fetal growth. On farm experience has indicated that colder winters are associated with higher birth weights. Other research has shown that maternal blood flow to the placenta is increased in cows exposed to colder temperatures, which may result in increased fetal growth. Cows in the summer group would experience much warmer temperatures during the last trimester of gestation than cows calving Feb/Mar. Since the utilization of feed sources (stored vs pasture) occurs differently with respect to the cows’ biological cycles, this could also have an effect on parameters like birth weight.

Another major difference between seasons was in the amount of assistance at calving. The Winter herd had a higher average calving ease score, indicating that they received a higher level of intervention. And the percentage of assisted births was much higher for the Winter group, for both cows and first calf heifers … Winter heifers were assisted 3.7X more than Summer heifers, while the Winter cow assist rate was 6X that of their Summer counterparts. As expected, the assist rate for cows was much lower than for heifers within each seasonal group.

Why the significant differences in calving ease scores and assisted births? Well , birth weight is one of the most important factors affecting calving ease, so its likely that part of the difference is related to the lower birth weights of the Summer group.

Another factor may relate to the environment that the animals were calving in. The winter group calved in small pens, indoors. Vigilance in winter calving requires regular pen checks, especially of cows that look “ready”. Checks were conducted between 5:00am and 10:00pm. This up close and personal interaction with the cows may inhibit their natural calving instincts and abilities. How many times have you checked a cow you were sure was about to calve, then gave it up for the night, only to find a fresh calf first thing in the morning? This may be even more important for heifers who are going through the calving experience for the first time.

In contrast, pasture calving cows were subject to a much lower level of human contact. The calving pastures were checked 3-4 times a day via truck or 4-wheeler. Typically, cows were left alone after dark. Finding a quiet spot away from other cows (not to mention people and bright lights) may have reduced psychological stress at calving and allowed cows to better express their calving abilities.

Another issue which probably plays a role is the “opportunity factor”. With barn calving, workers spend more time around the cows, and are more likely to observe cows in labour. This creates more opportunity to detect cows which seem to need assistance. With pasture calving, worker/cow interaction is reduced, so more cows calve without ever being observed in labour … so naturally, there would be less chance for workers to assist.

Table 2 shows that weaning rates (#cows weaning a calf / # pregnant cows retained) were similar for both groups of cows. However, the weaning rate for the Winter first calf heifers was lower relative to the Summer heifers. This was due to a combination of more fetal losses prior to calving, and a lower survival rate for these calves from birth to weaning.. Even though calving assistance was dramatically lower for the Summer group, it did not result in a significant reduction in calf survival.

There were major differences in calf health. We treated a lot more calves in the Winter group. On average, 33% of Winter born calves were handled at least once for treatment. This was more than double the 14% intervention rate for the Summer calves. And the Winter calves had a lot more repeat handlings. This gave an overall treatment rate of 2.8 Trts per Winter calf born, compared with only 0.6 treatments per Summer calf born. Although drug costs on a per dose basis were higher for Summer calves (due to the selection of more expensive, longer acting drugs) the total cost of drugs used for treatment of Winter calves was 3.3 X higher.

Why more treatments? Here are some of our ideas … despite excellent overall management, cows kept in confinement or semi-confinement housing tend to accumulate manure on the brisket, belly and udder. Newborn calves nosing along the dam’s underline are likely to suckle bacteria laden manure prior to making the colostrum connection. And as the calving season progresses, barns and yards become more contaminated. Add some mild weather to thaw things out, and it all adds up to a huge disease challenge for young calves.

In contrast, cows that have been on pasture for a month or two prior to calving present a much cleaner underline. Winter’s accumulation of manure has been shed along with the winter hair coat. In addition, pastures also present an environment which has much lower animal density, with reduced manure contamination and associated disease causing organisms.

So overall, pasture born calves are probably delivered into a healthier environment, and face less disease challenge than those born in confinement in winter. Added weight to this argument comes from the fact that the worst year for disease in the Winter calves occurred when access to outside yards was blocked due to construction. This would follow the accepted pattern of increased animal density = increased contamination = increased risk of calfhood disease.

Another potential factor affecting treatment rate could have been the ease of catching and handling the calves. Winter calves housed in pens are fairly easy to corral, relative to calves which are free to roam 25 acres. If this was the case, it would be expected to show up in higher postcalving mortality in the pasture born calves. But the results showed that while postcalving mortality was 1.9% for Winter calves, it was nil for Summer calves. So we didn’t appear to be missing sick calves on pasture.

Analysis of the amounts of straw use showed a substantial difference. When tallied on an annual basis, the Winter herd required 30% more straw (Table 3). A lot of this difference would likely be accounted for by the critical need for clean bedding at calving time.

Labour required for calving management was recorded for one year. Estimates indicated that the Winter group required about 35% more labour. Although Summer cows were spread over a larger area, making checking more challenging, they did not require the intensive calving pen management of the Winter herd.

So summer calving on pasture looks like a very viable alternative to winter confinement calving. These results from the New Liskeard Project showed several major advantages with the Summer system, with few drawbacks. But calving management is only one component of beef cow production … stay tuned for more results covering reproduction, cow and calf productivity, feed requirements and more!

In Summary …

This research showed that summer time calving on pasture can be a viable management practice. Compared with traditional winter confinement calving, the herd calving on pasture in summer had lower birth weights, received far less calving assistance, had a similar calving rate and lower postcalving death loss. Incidence of calfhood disease was much lower for the summer born calves, resulting in lower treatment costs. Additional advantages in the Summer herd were lower costs for bedding and labour at calving time.

Table 1. Calving characteristics of Seasonal Groups

Characteristic Winter Summer Probability
Birth Weight (lbs)1 105.6 99.5 P< .05
Calving Ease Score2 1.4 1.1 P< .05
% Assisted Births – Heifers 63 17 P< .05
% Assisted Births – Cows 18 3 P< .05

1 Adjusted for age of dam, sex of calf and birth type

2 Scale of 1-4, 1=unassisted, 2=easy pull, 3=hard pull, 4=surgical

Table 2. Health and Management Characteristics of Season Groups

Characteristic Winter Summer Probability
Intervention Rate (%) 33 14 P< .05
Treatments Per Calf Born 2.8 0.6 P< .05
Weaning Rate1 – 1st Calf Heifers 80 92.2 P< .05
Weaning Rate1 – Cows 96.3 92.7 NS

1 Weaning rate = # cows weaning a calf / # of pregnant cows retained

Table 3. Some Variable Costs for Seasonal Groups

Characteristic Winter Summer
Bedding ($/cow) 48 37
Calving Season Labour1 ($/cow) 41 30
Calf Treatment Drugs ($/calf born) $4.21 $1.28

1 Labour for pen or pasture checks, calving pen maintenance, calf processing and calf treatments


Tom Hamilton – Beef Program Lead (Production Systems)/OMAFRA


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