Some forage diets may need added nutrition for dairy cows

Dairy cows managed under low-concentrate input or organic farming regimens may require more feed energy for maintenance [pic: (c) istock.com]

Producers using a low input forage system may be underfeeding their lactating dairy cattle.

An international team of researchers reported results of trials examining nutrient requirements of dairy cattle on low forage proportion and high forage proportion input systems in the Journal of Dairy Science​.

The researchers examined the use of forage proportion (FP) on the metabolizable energy (ME) needed for cow maintenance (MEm) and the amount of ME needed for lactation, they said. Cattle getting larger amounts of forage may need supplemental nutrition.

“These results indicate that using the current energy feeding systems to ration dairy cows managed under low input systems may underestimate their nutrient requirements, because the majority of feeding systems adopted globally do not differentiate the maintenance energy requirements between low and high forage input systems,”​ they said.

Making forage comparisons​

Dairy farming using a low-input system has been popular in several areas with favorable grass-growing conditions, said researchers. However, in most systems, cows are fed on a high forage diet with little or no supplementation.

But, forages may not have the same levels of ME as a concentrate supplement, so cows need a larger amount of forage-based feed, they said.

“The greater physical intake required with a forage-based diet to achieve similar levels of ME intake are likely to result in greater gut fill, an increased energy expenditure on rumination and digestion, and a greater production of acetic acid in the rumen,”​ they said. “All of these factors can contribute to an increase in gut mass, an increase in the size of other internal organs, and a higher metabolic rate.”​

Previous research using calorimeter chambers suggested that cows have additional ME needs for maintenance, they said. But, current systems do not consider the influence that diet forage proportion has on metabolic rates.  

“The objectives of the present study were to use a large calorimeter data set of lactating dairy cows collated at this institute [Agri-Food and Biosciences Institute]​ to investigate the influence of diet FP on energetic efficiency, and to quantify any differences in MEm and the efficiency of ME use for lactation (kl) for lactating dairy cows offered diets containing low and high proportions of forage,”​ said researchers.

Experiment​

In the experiment, 930 cows were offered different diets for five to eight days depending on the trial, said researchers. The diets included a forage-only ration, and forage with concentrates where the FP amount ranged from 18% to 100%.

The cows were divided into four groups based on the amount of forage proportion they received, said the researchers. The groups included FP<30%, FP=30-59%, FP=60-99% and FP=100%.

Forages were comprised of grass, straw, corn silage, wheat silage and alfalfa. And, concentrates included cereal grains, protein meal or grain by-products.

“The MEm for individual cows was calculated from heat production minus energy losses from inefficiencies of ME use for lactation, energy retention and pregnancy, and kl was obtained from milk energy output adjusted to zero energy balance (El(0)) divided by ME available for production,” ​said the scientists.​

Total feed intake was noted, and manure and urine were measured and sampled, they said. Animals spent the last two to four days of the study in a calorimeter chambers.

Results​

Increasing amounts of forage proportion reduced the ME intake and limited milk energy output, said the researchers. Differences were less noticeable between the two lower FP groups.

Cows getting the higher FP diets had a higher ratio of heat production over ME intake and MEm, said the scientists. However, the differences between the two low FP groups weren’t significant for heat production/ME intake nor were there differences between the two higher groups for MEm.

Diets with higher amounts of FP limited dry matter intake, body weight and the amount of energy corrected milk produced, they said.

“The FP = 100% group had a significantly lower ME/GE [gross energy] and ME/DE [digestible energy] than the other 3 groups (P < 0.001),”​ they said. “Increasing diet FP significantly increased HP/ME intake, and reduced El/ME intake.” ​

Lactation values were similar for all four groups, they added.

When a linear mixed regression analysis was used on the zero energy balance to ME intake the net energy requirement for maintenance increased as FP rose, said researchers.

“It is concluded that increasing diet FP had no effects on kl but significantly increased maintenance energy requirement,”​ they said.

“The present result indicates that dairy cows managed under low-concentrate input or organic farming regimens may require more feed energy for maintenance than those reared in high-concentrate input systems,”​ they said. “Using the current energy feeding systems to ration dairy cows managed under low-concentrate input systems may underestimate their nutrient requirement.”​

The research was supported by a grant from European Union’s Seventh Framework Program.