Advancing young stock performance: pre and post-weaning

Courtesy of his presentation, Aaron Brown, Technical Sales Manager with Trouw Nutrition, specifically characterised the maturation of the rumen at two levels: the growth of the muscular wall that surrounds the organ and, in addition, the multiplication of the epithelial layer that directly interacts with the nutrients ingested by the animal.

The greater the development of the epithelial layer: the greater the ability of a young animal to absorb nutrients and to grow. Aaron pointed out that the presence of butyrate is directly associated to the development of the rumen in calves. This is linked to the presence of starch in the diet, therefore driven by concentrate intake.

The Trouw Nutrition representative defined weaning as the transition-off a milk-based diet. There are a number of ways in which this can be monitored. One is directly associated with young calves reaching the stage when they are consuming at least 2kg of concentrate, consistently, on a daily basis.

“Others highlight that appropriate time of weaning is when calves have consumed approximately 32kg of concentrate from birth, indicating adequate exposure of the rumen to starch. However, there are two overarching criteria that should be met: weaning must be a gradual process and it would be unwise to wean a calf before it has reached eight weeks of age.

“The transition to the weaned state must be managed to ensure calves receive their full energy requirement to sustain growth and not compromise daily live weight gain.”

Maximising concentrate intake from the earliest possible stage in the calf’s life is critically important. Aaron discussed a number of factors that directly impact on this issue.

Water

“Young calves must have access to clean water from the outset. The bacteria that are required in the rumen to drive its development live in an aqueous environment. This being the case, drinkers should be cleaned regularly. Trials have indicated that drinkers located at the back of pens tend to get dirty much faster than those placed at the front. Cleanliness not only impacts disease exposure but also palatability.”

Aaron continued: “It is also imperative that milk intakes are not restricted for the sake of solid feed intake during the first four weeks of life; during this period solid feed intake is negligible regardless of milk allowance so milk intake should be the priority to ensure adequate consumption of nutrients. Research trials have confirmed that restricting milk will also compromise immunity in young calves when faced with a disease challenge.”

Forage

Having access to a high-quality forage is also important for calves at all stages in their development. Straw, as opposed to hay, is the preferred forage source of calves.

“Hay will deliver increased weight gains in calves. But this tends to be a result of increased gut fill only,” Aaron commented.

According to the Trouw representative, forage availability minimises the risk of acidosis when pellets are offered to young calves. The larger particle size of the forage source also delivers a scratching effect, which helps to clean the epithelial wall. If this is not achieved, the absorption capacity of the developing rumen is reduced. Chopped straw with a particle size of five centimetres or less is ideal.

“Concentrates should be offered on an ad lib basis to young weanlings in the weeks directly after weaning to maximise nutrient intake levels maintaining their large energy demand.”

Other factors impacting on starter intake are the actual composition of the concentrate offered, house design and grouping of calves.

Aaron Brown again: “Starter feeds should be in the range of 16% to 18% protein, having high levels of starch. Trials have confirmed the benefits of adding Sodium Butyrate to calf starter products can encourage starter intake. Where housing is concerned calves should have access to 30cm of trough space per head. Light duration in sheds will also have an impact on the length of time that calves remain feeding.

“Autumn born calves will respond to lighting periods that correspond to those that predominate during the spring and summer months of the year. Research has also confirmed that calves experience less stress when grouped together. So, the faster this can be achieved the better the performance levels that can be secured.”

Calving replacement dairy heifers at 24 months

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.

“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”.

“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.”

Worming strategies at grass

Zoetis veterinarian, Patricia van Veen, informed the seminar that stomach worms continue to have a significant impact. An EU-wide study published in 2020 estimated that gutworm, lungworm and liver fluke infections cost the UK cattle industry an estimated £227M* annually.

Her key take-home message centred around the benefits of working as a team with your advisors and prescribers to optimise the outcome for the grazing season.

The success of the grazing season starts with a healthy animal in good condition at turn-out, one that can respond well to the worm challenges during grazing. It is important to find a balance between acceptable levels of worm burdens, pasture contamination, immunity to worms and treatments.

The two main parasites involved in parasitic gastro-enteritis (PGE) in cattle are Ostertagiaostertagi and Cooperiaoncophora. Youngstock can show signs of diarrhoea, weight loss and decreased feed intake during PGE in their first grazing season.

The veterinarian also confirmed that disease from lungworm remains unpredictable and can result in severe disease and death. Youngstock at grass for the first time are more predisposed to lungworm disease until immunity has developed. Lungworm vaccination is an important tool on any farm with a history of lungworm disease.

The life cycle of the parasite is facilitated by fungi that inhabit dung pats. They act to physically disperse larvae onto the surrounding grass and allow larvae to travel over large distances into neighbouring fields. The risk of disease from lungworm infection is highest when rain follows a dry spell in late summer. The rain and humidity disperse worms from dung pats and a sudden increase in larvae results in sudden severe worm burdens and lung damage.

If lungworm has been a problem on a farm, it is important to monitor cattle closely during these periods. Any sign of coughing in late summer should be taken seriously, and youngstock should be moved from the field to safe grazing. Treatment should be considered carefully, as the worm treatment of choice can be different for individual farms.

Patricia van Veen again: “Worming strategies can be planned around those times during the grazing season when cattle are gathered for routine management procedures. Planned grazing should also allow for safe pasture to be available at high-risk times, as mentioned for lungworm.

“Taking dung samples and for faecal egg counts (FEC) will deliver important information on the need and timing of stomach worm treatments. Quarantine measures are particularly important where store cattle are bought-in.”

Looking to the future, Patricia notes that anthelmintic resistance will become an increasing challenge.

“A lot of work is being done by groups like COWS, to develop guidance for farmers and their prescribers.

“There are some useful tools available to help understand the different wormer groups; white 1-BZ, yellow 2-LV or clear 3-ML. We should use anthelmintics responsibly so that they remain effective into the future.

Reference: * Charlier, J., et. al. Preventative Veterinary Medicine. 2020