The impact of feed conversion ratio and feed efficiency on profitability of dairy farming

Feed conversion ratio for cattle has a big impact on feed efficiency in ruminants. Cattle feed efficiency is an important performance indicator for a dairy farm. Improve feed conversion and profitability and sustainability of dairy farming will increase. The feed conversion ratio for cattle is most commonly defined as the amount of protein and fat corrected milk that a dairy cow produces divided by the amount of dry matter she consumes. It is however also possible to express feed conversion efficiency as the amount of fat and protein corrected milk produced per unit of nitrogen fed, per unit of energy fed or per unit of methane produced. Lastly, if efficient use of arable land is an issue, feed conversion ratio can be calculated per hectare of pastureland, instead of calculating feed efficiency in ruminants.

Cows with a higher feed efficiency generate the same amount of milk as the rest of the herd while consuming significantly less feed. Feed conversion ratio in lactating cows can vary from <1.3 to >2.0 (See table 1). When comparing feed efficiency of dairy herds, it is important to compare "like for like". If feed conversion efficiency is being calculated in the US, fat and protein corrected milk yield is usually calculated towards 3.5% fat, whereas in Europe it is more common to calculate feed conversion ratio on milk corrected towards 4.0% fat.

According to the FAO, livestock production is responsible for 14.5% of all global greenhouse gas emissions. Within that, the dairy sector accounts for about 2.2% of the greenhouse gas emissions. Feed conversion ratio of cattle is therefore an important driver of sustainability. A high correlation has been found between feed efficiency in ruminants and production of greenhouse gas (see Figure 1). If farmers improve feed conversion of their cows, they will not only improve dairy feed cost efficiency, their cows will also produce less greenhouse gas per kg of milk produced.

Factors that can influence feed efficiency of dairy cows include milk production and component yield, feed intake, forage quality and quantity, cow age, ration protein levels, composition of the diet, body weight, environmental stress, exercise, pregnancy, poor udder health, subacute rumen acidosis, problems with hindgut health and "leaky gut", other health issues and feed additive use. Out of those, important factors that improve feed conversion are:

• Milk yield and days in milk, highly productive dairy cows have a better feed conversion ratio
• Feed quality, if digestibility of feed is increased, cattle feed efficiency increases also
• Somatic cell count has an impact on feed efficiency because poor udder health of dairy cows can result in lower milk yields
• Subacute rumen acidosis and hindgut acidosis affect digestion, impede feed passage and reduce energy partition and feed conversion efficiency of dairy cows.

Milk yield has a big impact on feed conversion efficiency, because the amount of energy required for maintenance is not dependent on the milk production level of a dairy cow. As a result, highly productive dairy cows have a better feed conversion ratio and thus a higher cattle feed efficiency (see table 2). This also means that the number of days in milk has an impact on feed efficiency in cattle, with cows lower feed conversion efficiency during the 2^nd half of lactation.

Digestibility has a big impact on feed efficiency in ruminants, because more digestible feeds release more energy and protein per kg DM, so feed conversion ratio will go up (see Figure 2).

The newly revised NASEM 2021 guidelines for dairy cows have different dietary protein ration requirements compared to the NRC guidelines for dairy cows. Following these guidelines will improve dairy feed cost efficiency. An improved understanding of the role that metabolizable protein (MP) plays for lactating dairy cows has established new relationships between protein in the diet and milk yield. To improve feed conversion of dairy cattle, ruminal microbes need amino acids and peptides, but ammonia can also be an important nutrient for ruminal microbes. Ammonia can be provided by a range of sources including grass silage and urea. Different sources of nitrogen can have a different impact on nitrogen feed efficiency in ruminants. Sources of amino acids include rumen degraded microbial protein, rumen undegraded protein (RUP) and rumen protected amino acids. Among amino acids, several are considered essential but are not provided at required levels within most feed ingredients. This could potentially reduce feed conversion ratio. Many feed ingredients for dairy cows have enough of one, but not all amino acids. In those cases, the use of rumen-protected amino acids can improve feed efficiency in ruminants, because it results in an increase in milk production with higher protein and fat levels.

The amount of milk urea nitrogen (MUN) is indicative of the ability of the rumen microflora to convert ammonia into microbial protein. Increased MUN levels are indicative of poor rumen function. Poor rumen fermentation will result in a reduction of fertility and feed efficiency in cattle.

Somatic cell counts of dairy cows are indicative of subclinical udder infections. Inflammation of the udder results in loss of milk production and a reduction of feed conversion efficiency. A Dutch study114 showed that subclinical mastitis in heifers has a negative effect on dairy feed cost efficiency. Each case of subclinical mastitis in a heifer results in loss of production of 0.28-0.31 kg of milk/day. A case of subclinical mastitis in multiparous cows has an even bigger impact on cattle feed efficiency, it results in a loss of 0.50-0.58 kg of milk/day. Feed efficiency was also studied in cows suffering from subclinical mastitis. In a Danish study115 milk loss in animals suffering from subclinical mastitis in an entire lactation of 305 days was 155 kg of milk in primiparous dairy cows and 445 kg of milk in multiparous dairy cows. Subclinical mastitis therefore has a big impact on dairy feed cost efficiency as well.

Subacute ruminal acidosis (SARA) and hindgut acidosis are common problems in lactating dairy cows that cause chronic health problems, impair cattle feed efficiency, and increase the environmental impact of milk production. Low ruminal pH appears to be the main instigator of the pathophysiology of SARA, although other metabolites produced in the rumen may be involved. Inflammatory responses to SARA are variable but important determinants of a cow's response to SARA. The same factors that increase the risk for dairy cows to develop SARA (e.g. low forage diets with high levels of starch) can also lead to problems with hindgut health and “leaky gut”. Prevention of SARA and hindgut acidosis can improve feed conversion efficiency in dairy cattle,but this requires excellent feeding management and proper diet formulation.