Achieving High Calf Weaning Weights

Associate Professor Steve Morris
Institute of Veterinary and Animal Sciences
Massey University

The ability to wean heavy calves has become progressively more important in conventional single-suckled breeding-herds because with the trend towards marketing at a younger age, growth to weaning represents a higher proportion of the total growth to slaughter.

Weaning weight is a function of

• Breed of dam and sire (also their genetic merit)
• Milk production of the dam
• Age of dam
• Level of nutrition of cow and calf
• Age of calf
• Calving date

This article will concentrate on milk production of the dam, cow and calf nutrition, calving date and calf age at weaning.

Calf weaning weight targets will be specific to the farm in question but a minimum liveweight gain target for a suckled calf on hill country would be 1.0 Kg/calf/day. Most beef calves are usually weaned at around 5-7 months of age resulting in calf weaning weights of a minimum of 180 - 240 Kg at weaning (assuming a 35 kg birthweight). The importance of calving early (target of 70 % of cows calving in the first 21 days of calving) within an appropriate calving period (where the planned start of calving is correctly timed to pasture supply) can not be underestimated through its effect on calf weaning weight and cow re-breeding performance. Many commercial beef herds are calving far to early in the spring. The usual sign for this is a slow start to calving i.e. less than 50% calved in first 21 days of calving, and represents a major factor compromising calf weaning weights and cow rebreeding performance.

The best cow for hill country is a medium sized cow that weans a high proportion of its liveweight in calf weaning weight. A rider to this is that cow is in good condition (score 3 +) at weaning and can then use her excess condition as "supplementary feed" over the winter months. In fact cows should be at their maximum liveweight and condition at weaning indicating they have eaten a high proportion("conserved") of the excess summer feed that usually occurs on hill country properties. Cows should therefore wean calves that weigh 50 to 60 % of the cow's weight. This is not a new concept as Bratcher (1968) reported in the New Zealand Aberdeen Angus Review (Volume 2, page 8) that smaller cows wean a higher percentage of their bodyweight in calf, particularly if they are good milkers like the Angus. He further stated that it is not uncommon for a 450 kg Angus Cow to wean a 225 Kg calf in 205 days and that individual cows reared up to 60% of their weight in calf.

The rate of growth of the suckling calf largely depends on the cow's milk supply, which in turn depends on the food available to her. In fact some researchers indicate that about 70% of the variation in weaning weight of calves is due to differences in milk production of the dam. The calf has a limited capacity to consume milk early in lactation so there is no merit in having cows producing more than 8 kg milk when a 50 Kg calf can only drink 7-8 kg per day. It seems about 8 kg milk will convert to 1 kg calf gain per day. Hence milk alone will meet the target of 1.0 kg/LWG/day in early lactation but once the calf reaches the fourth month of lactation this amount of milk will only supply enough nutrients for 500 grams/day for a 150 Kg calf - hence the need for the calf to consume pasture.

It has been estimated that a calf is able to consume milk daily amounting to 10-15% of its liveweight. Thus a calf weighing 35 Kg at birth would consume around 4-5 kg milk while a calf at 120 days weighing 150 Kg could consume around 15 Kg of milk. It is highly unlikely a cow would produce that much milk at that stage and so the calf gets its extra nutrients from pasture consumption.

To achieve high calf weaning weights cows must be well fed before and after calving. A high level of feeding after calving is also necessary for a high conception rate at rebreeding. Experience suggests that a feed budget should allow for a cow to eat in excess of 12 Kg DM/day from the day of calving. How this will be achieved depends on the date of calving but in most situations it will involve the need save feed forward from late winter. Cows will often buffer their calves against underfeeding in early lactation by losing liveweight to maintain calf growth. But this can not happen in poor conditioned cows (Condition Score 2 or less). It is therefore desirable to have cows in a condition score of 2.5 or better at calving. A recent trial at Massy University indicated that for heifers a sward (pasture) height of 6 cm is sufficient in the first month after calving increasing to 10 - 12 cm during the second month.

Date of weaning should depend on feed supply (it often depends on labour convenience and sale date). If there is ample feed there is little to be gained from early weaning unless there is opportunity to use the cows in a mob for pasture control or preparation for other classes of stock. However, if hill country pastures dry out badly in summer, calves could be weaned and put onto what fresh pasture is available and the cows fed hard rations to relieve grazing competition.

In conclusion hill country beef cows must consistently produce a high ratio of their own liveweight as a calf at weaning while also contributing effectively to pasture supply and quality management of hill country pastures.