When dairy cows are fed diets with reduced protein concentrations – aimed at decreased environmental nitrogen pollution from their manure such as nitrate leaching, nutrient-laden run-off and ammonia volatilization – their milk production can suffer. Supplementing the amino acid histidine may help in maintaining, and even increasing, milk and milk-protein yields. That’s the conclusion of a new study conducted by an international research team led by Alexander Hristov, a senior researcher at Penn State University. The researchers recently published their findings in the Journal of Dairy Science. Histidine is an essential amino acid for protein synthesis, Hristov explained. He added that earlier studies in Europe have shown that low histidine levels can limit milk production in dairy cows fed diets based on grass silage, which is the predominant forage in Northern Europe. Limited histidine was not considered a challenge for dairy cows fed typical North American diets until research conducted in Hristov’s lab in the College of Agricultural Sciences at Penn State a few years ago revealed the problem. In those experiments, blood histidine concentrations dropped significantly when cows were fed reduced-protein diets aimed at curbing nitrogen losses and ammonia emissions from manure.

The recently published series of experiments also confirmed the importance of histidine to maintain milk production and milk protein content when cows were fed diets with reduced protein concentration. “The culmination of this research was the recently published meta-analysis of 17 studies which concluded that histidine supplementation of dairy cow diets increased feed dry matter intake, milk yield and milk protein concentration,” Hristov said. “Notably, and as Penn State research has shown, the increase in milk protein concentration with histidine supplementation was up to four times greater for cows fed diets that had lowered protein content than diets formulated to provide adequate protein intake, according to diet-formulation models.” Histidine is unique among the essential amino acids because there are body reserves that can serve as sources of histidine and mask short-term deficiencies, Hristov said.

For that reason, histidine effects in dairy cows should be studied in long-term, continuous-design experiments. “Further, microbial protein synthesized in the rumen – which is the main source of amino acids for the cow – is low in histidine, relative to other potentially milk-limiting amino acids,” Hristov said. “That supports our hypothesis that histidine becomes the first limiting amino acid when cows are fed low-protein diets. So, the role of microbial protein as a source of amino acids for milk protein synthesis and body functions becomes even more critical.”

Coccidiosis is an intestinal disease caused by unicellular parasites that usually occurs in young dairy or beef calves between 3 weeks and 6 months of age. Although it is rarely fatal, it can cause extensive gut damage and ill-thrift and is commonly seen under intensive management conditions with high stocking rates.

Autumn-born calves are at greater risk, with Cocci requiring warmth and moisture. A wet September and October increases infection risk as the environment becomes more favourable for the occysts to spread from calf to calf.

Veterinary specialists Murray Direct said calves become infected by consuming coccidiosis eggs from pasture, feed, waste and bedding, or by licking contaminated calves. The parasite can exist for months in their surroundings and failure to control the disease can influence future productivity levels, including growth rates, as well as delaying the onset of puberty, leading to milk loss production in dairy calves.

Third-generation dairy farmer, Darren Coombes, who farms with his son Tim on 890 acres near Bridgwater, Somerset in the UK, believes feeding a coccidiostat to his dairy calves can help control the disease. He recently had an outbreak affecting a fifth of his calves. 

Coombes milks 425 cows – year-round calving Holsteins – supplying Muller and Sainsbury’s. Animals are milked twice daily, producing 10,500 litres at 4.3% fat and 3.25% protein.

“We didn’t lose any calves, but we lost a lot of growth and it took the calves a long time to recover,” he said.

His vet recommended the calves be fed the coccidiostat Deccox and, alongside improved cleanliness, it has helped get on top of the outbreaks.

Coombes said newborn calves receive colostrum for the first 3 days. Calves are kept in pens for the first week and at day 4 they transition onto a milk replacer with 3 litres fed in a bottle twice a day. From birth, calves are given clean water and free access to fresh straw and Mole Valley Farmers’ NSP NPP Calf Rearer 18+ Deccox, which is an 18% protein rearer nut with an added coccidiostat to help treat and manage coccidiosis.

“It is a very consistent, palatable product and calves love it. After 7 days, calves move onto one of the 2 Forster-Technik automatic milk feeders where they are kept in groups of 30. Calves get fed 4 feeds a day and can have a maximum of 8 litres in 24 hours. At day 49, the milk is gradually reduced and calves are weaned at day 56.”

Calves stay in the same group until they are 6 months old. After 5 months they are introduced to 1kg of homegrown rolled barley and ad-lib grass silage with the rearer nut cut back to 1kg. Deccox is removed at 9-10 months. Coombes notes: “It has completed kept coccidiosis at bay. We tried different things and we could never really get to the bottom of it until we introduced the Deccox.”

But hygiene is key, too. Calf sheds are disinfected and steam-cleaned between batches and straw bedding is also replenished liberally to keep calves dry.

Andy Adler of Molecare Farm Vets said preventing faecal contamination of water and feed troughs is crucial in controlling coccidiosis. “Raising feed and water troughs alongside regular cleaning is very important to prevent faecal-to-oral transmission. Straw bedding should be replenished often so calves are only eating fresh, clean straw.”

Scientists have collaborated to produce the first gene-edited calf with resistance to bovine viral diarrhoea virus (BVDV). The study, published recently in PNAS Nexus, is the result of a collaboration between several universities and industry players. BVDV is one of the most important viruses affecting the health and well-being of cattle worldwide and has been studied by researchers since the 1940s when it was first identified. The virus does not affect humans, but is highly contagious among cattle and can cause severe respiratory and intestinal disease. BVDV can be devastating to pregnant cows, as it can infect developing calves, causing spontaneous abortions and low birth rates. Some infected calves survive to birth and remain infected for life, shedding massive amounts of virus to other cattle. Over the past 20 years, the scientific community has discovered the key cellular receptor (CD46) and the site where the virus binds to this receptor and causes infection in cows. In this latest study, scientists have modified the virus binding site to block infection. Aspen Workman, lead author and researcher at ARS’ US Meat Animal Research Center (USMARC) in Clay Center, Nebraska, said, “Our goal was to use gene-editing technology to slightly modify CD46 so that it doesn’t bind the virus but still retains all its normal functions in cattle. The scientists first tested this idea in cell culture. After seeing promising results in the lab, Acceligen edited cattle skin cells to develop embryos carrying the modified gene. These embryos were transplanted into surrogate cows to test whether this approach could also reduce viral infection in live animals. It worked, and the first CD46 gene-edited calf, named Ginger, was born healthy on 19 July 2021. The calf was followed for several months and then challenged with the virus to see if it could become infected. She was housed for a week with a BVDV-infected dairy calf that was born shedding virus. Ginger’s cells showed significantly reduced susceptibility to BVDV, resulting in no observed adverse health effects. Scientists will continue to monitor Ginger’s health and ability to produce and rear her own calves. This promising trait is still in the research phase and no associated cattle are currently entering the US food supply.