11 June 2013

6 minute read

Pasture calving offers a viable alternative to housed methods and produces robust calves through a method that requires less intervention, says the Ontario Ministry of Agriculture and Food. 

Its calving time! That phrase strikes fear and trepidation into the hearts of many cow-calf producers. Few things on the farm produce as much drawn out stress and as many sleep interrupted nights as ensuring the safe delivery of this year's bawling "cash crop". The popular Mar-Apr calving season leads to a constant battle against the weather, the build- up of manure in the maternity pens and yards, and all too often, an intense skirmish with scour causing pathogens.

New Liskeard Calving Systems Trial

At the New Liskeard Agricultural Research Station, a calving systems trial was initiated in 1992. At that time, the herd was split into two management groups. One group in February-March in a modern open front barn with separate calving pens, while the other group calved on pasture in June-July.

Data collection was intensive, and along with the usual animal performance records and health data, feed consumption and the labour required to manage the herds was also collected. The trial ended after 5 years, and during this time it was found that pasture calving cows received far less assistance at calving and raised healthier calves than barn calvers. There was a lower labour requirement for the pasture calving herd, while stored feed consumption was similar. The weaning weights of pasture calving cows were somewhat lighter, but economic analysis showed that the overall, the cost of producing a pound of weaned calf was much lower for the pasture calving herd.

Figure 1. Housing for winter calvers

After the end of the formal experiment in 1997, the two calving groups were maintained, and all of the animals were used in numerous experiments over the years. However, a large database of animal performance an health records were collected from 1998 on. In 2012, the Ontario Cattlemen's Association (aka Beef Farmers of Ontario) requested that the herd management data accumulated over time be analysed and reported. OCA(BFO) have a direct interest in the New Liskeard Herd, since they own all of the cows and their progeny.

The Data Set

A total of 3293 females were exposed to breeding over 15 years, with 1673 in the Winter group and 1620 from the Summer group. These were comprised of 2344 cows and 949 heifers. All breedings were by AI, typically with an initial round of fixed-time insemination followed by a resynchronization of those not bred. Cows were usually checked for pregnancy twice, and initial check to evaluate the first insemination and a final check to evaluate the second insemination.

Figure 2. Summer calvers on pasture

Pregnancy Rate

Result so the final pregnancy check are shown in Table 1. Overall, the animals bred to calve in Winter had a small (3.3 per cent ) but statistically significant advantage over those bred to calve in Summer. When evaluated on an age group basis, only the difference in cow groups was significant.

From Figure 3, a couple of trends can be identified. During the first 3 years, the Summer group had numerically superior pregnancy rates, but in general this was reversed during the remainder of the trial. Higher pregnancy rates for Summer calvers were observed during the 5 year formal trial. Reasons for the change observed in this evaluation may be related to the disproportional use of young sire semen in the Summer calving herd, as part of a strategy to accelerate genetic change. It is known that the fertility of yearling bull semen is generally lower than that of older bulls.

Another trendapparent in Figure 3 is the reduction of breeding success as time progressed. This may be attributable in part to the introduction and increasing use of yearling sire semen in both groups, and may also be in part due to changes in the methods of fixed-time synchronization techniques used.

Pregnancy score:1= pregnant, 2= not pregnant; score of 1.2= 20 per cent open
Figure 3. Comparison of Pregnancy Rate to Final Preg Check, by Season

Calving Ease

Calving ease was recorded as unassisted, easy pull, medium pull, hard pull or surgical. These were converted to scores (1 to 5, respectively) for analysis.

Calving ease score was higher for the Winter born calves (1.15) than for Summer born calves (1.06) showing that there was lower incidence and/or severity of calving problems in summer (Table 2). This showed that calving on pasture can result in fewer and/or less severe calving problems than barn calving. This is likely due in part to lower average birth weights in the Summer group. It may also be partly due to an increased ability of cows to give birth in the pasture environment, and/or the reduced opportunity for humans to intervene.

The rate of calving assistance was also evaluated, by grouping calving outcome into two categories, either unassisted or assisted. Average assist rate for the Winter group (7.8 per cent ) was more than double that of the Summer group (3.0 per cent ) (Table 2). This is likely due partially to the lower birth weights of summer born calves and also to the reduced opportunity for herdsmen to intervene when cows were on pasture. As well, it is possible that cows calving on pasture within sight of other cows and in a more natural environment are less psychologically stressed and better able to express their natural calving ability.

Calf Health

Disease occurrence and treatments of calves from birth to weaning were obtained from NLARS herd health records from 2005 - 2012. These data were summarized to give both the number of separate disease occurrences and the total number of treatments administered (Table 6).

For example, a calf identified as having pneumonia and treated on 4 consecutive days for it would be classed as having 1 disease occurrence and 4 total treatments. One calf could have multiple disease occurrences (and additional treatments) over time.

The results showed that Winter-born calves had an incidence of disease which was 3 times that of Summer-born calves, and a total treatment rate which was 2.25 times higher than Summer calves. One reason for this difference may be due to a higher density of animals in the barn environment, which would promote a greater build-up of pathogens compared with the pasture environment.

This would likely present a greater disease challenge to the calves born in the barn environment. As well, Summer calving cows had less manure tag on them than Winter calving cows (pers. obs.), which should lead to less transfer of disease causing organisms to the calf during initial suckling attempts.

While it is theoretically possible that pasture born calves may have received fewer treatments simply due to less intense observation than barn born calves, this is unlikely since their survival rates were not different, and the average weaning weight of barn born calves was only minimally greater.

Calf Survival

Calf survival was calculated as the proportion of calves weaned compared with the number born. Calf survival was high, and not different between seasons. This showed that although the Summer calving herd was managed under a much more extensive regime, with less human observation during the critical neonatal period, calf survival was not compromised.

Conclusion

The results of this review of 15 years of data supports the earlier findings in terms of calving ease and calf health. Pasture calving is a viable production system which requires far less intervention at calving time and produces healthier calves which require far few treatments. Cows can calve successfully with little intervention in the "Green Maternity Ward". Producers wanting to reduce the need for observation at calving time and/or expand their cow herds should consider a production system based on summer calving on pasture.

June 2013