United Feeds’ nutritionist, Jenny Hamilton, confirmed that the onset of puberty is generally determined by heifer weight as opposed to age. And although weighing replacement heifers is the most accurate measure, it’s not often practical.
She further explained: “Bodyweight and height at the withers are closely correlated with one another. So having a height gauge placed into a handling pen, or a measuring stick with you can take with you, while checking youngstock at grass, is one effective way of monitoring growth throughout the grazing season. It also ensures that skeletal growth targets are being met.
Target daily weight gain for calves post weaning up to 13 months should be 0.8kg per head per day. This figure reflects the growth rates required for heifers that will mature into cows weighing approximately 650kg.”
Jenny continued:
“We don’t want an animal that will be reaching puberty at too late an age. We need to have heifers successfully bred by 15 months to achieve a 24 month calving age. Neither do we want replacement heifers to be too small in stature. This is why the regular monitoring of replacement heifers at grass is important.
The post-weaning diet should supply sufficient protein and energy to facilitate muscle weight gain and skeletal development. Grazing high quality grass can be a cheap and effective way of achieving this. However, we need to be mindful that post-weaning the rumen is still developing and not able to process forages fully and has a limited capacity. So, concentrate supplementation in the first summer at grass is essential to ensure we meet our liveweight targets.”
United Feeds’ Ruminant Nutrition Advisor, Sean Roddy, explained that grassland management should aim to firstly, secure the highest possible daily gains while managing grass utilisation and secondly, maximise the number of grazing days.
He continued: “For calves we are looking for a grass cover in the range of 2,500kg to 3,000kg of dry matter per hectare. For younger claves slightly heavier covers heading towards the 3000kg/DM/ha will work as the animals are getting that little bit of extra fibre intake, provided they are grazing down well, aiming for a residual of 2000kg/DM/ha. For older calves aim for a residual closer to 1600kg/DM/ha.
According to the United Feeds’ representative, “young calves should be moved on to fresh grass every three to four days. Calves can struggle to graze out fields effectively if the rotation length is longer than this. He referred to an AFBI study where rotationally grazed heifers gained an extra 0.04-0.16kg/day over their continuously grazed counterparts” he commented.
“Silage after grass should also be included in the grazing rotations of older calves. Taking this approach helps boost the quality of the grass available to youngstock, and crucially reduces the worm burden on these animals.
“Implementing a leader: follower system also helps to get fields grazed out.”
Where calves are concerned, Sean Roddy strongly advises that animals should not be turned out to grass hungry.
He further explained: “When these animals are first turned out, they will run around and explore for a while. So, in effect, it could take a number of hours before they start eating.
A good rule with stock of all ages is this: if you are changing the diet, don’t change the environment. Alternatively, if you are changing the environment, don’t change the diet.
In other words, don’t change everything at the same time. So if calves have been on nuts and straw in a shed, the same diet should be available to them, initially, in the field, until such times as they fully transition on to grazed grass.”
Sean concluded:
“The same principle holds where autumn born calves are concerned. Although they will be able to replace silage with grazed grass quite quickly, it’s beneficial to keep straw available to calves of all ages when turned out to grass initially.
Subsequent performance at grass will be determined, to a very large extent, by the level of performance secured prior to turnout. However, managing the transition to a grass diet, and not reducing concentrate feed rates until grass intakes are a significant proportion of the diet will help maintain performance.”
