Dr. David Lalman, Oklahoma State University Professor and Harrington Chair, Extension Beef Cattle Nutrition Specialist regularly offers reports as part of the weekly series known as the “Cow Calf Corner,” published electronically by Dr. Peel and Mark Johnson. Today, Dr. Lalman is addressing feed intake for mama cows.
In the September 16, 2024 edition of the Cow-Calf Corner Newsletter, the widely adopted equation to estimate feed intake in beef cows was discussed. That equation was published in 1996 in Nutrient Requirements of Beef Cattle, Seventh Revised Edition, National Academy of Sciences, Engineering, and Medicine (NASEM, 1996). Another widely used guideline for beef cow feed or forage intake was published by Dr. Chuck Hibberd and Dr. Todd Thrift in 1992 (Table 1).
| Table 1. Forage capacity of beef cows | ||
| Forage quality | Stage of production | Dry matter intake % body weight |
| Low quality forage< 52% TDN | Dry | 1.8 |
| Lactating | 2.2 | |
| Average quality forage53 to 59% TDN | Dry | 2.2 |
| Lactating | 2.5 | |
| High quality forage> 59% TDN | Dry | 2.5 |
| Lactating | 2.7 | |
In her effort to test these guidelines, along with the 1996 equation, Megan Gross used 85 study or treatment means. She restricted this “validation” data set to include studies published that met the following restrictions:
- Data either published or studies conducted between 2003 and 2022.
- Cows had ad-libitum (free choice) access to feed.
- No marker generated data.
- No metabolism or tie stall data.
- Only studies with adequate dietary protein were included.
As a sidenote, 58 of those 85 treatment means were generated by our group at Oklahoma State University.
Like the 1996 NASEM equation, the Hibberd and Thrift guidelines are sensitive to body weight, diet digestibility or energy, and stage of production. Megan discovered that these guidelines consistently overestimated dry-cow feed intake. In fact, the average deviation from the observed values was about 6 pounds per day with slightly better accuracy when diet digestibility was low and slightly poorer accuracy when diet digestibility was high. As a reference, the NASEM 1996 equation had an average deviation from observed values of 5.3 pounds per day in dry cows.
The Hibberd and Thrift guidelines were substantially more accurate in estimating lactating cow feed intake with an average deviation from observed values of about 3.3 pounds of feed or forage per day. That compares to 6.6 pounds average deviation from observed values using the NASEM, 1996 lactating cow equation. Certainly, reasonable estimates of feed intake in lactating beef cows can be obtained using the Hibberd and Thrift guidelines.
The feed intake equation developed using the more recent data is provided below. Intake must first be calculated using metric units (kg), but then can be converted to imperial units (pounds) by dividing kg per day by 0.454.
Dry cows: DMI = SBW0.75 * 0.017 + Diet NEm * 1.18 – 14.38
Lactating cows: DMI = SBW0.75 * 0.017 + Diet NEm * 1.18 – 11.1
Where DMI is dry matter intake, kg per day; SBW0.75 is shrunk body weight raised to 0.75 power; and diet NEm is diet net energy for maintenance, megacalories per kilogram of feed. Shrunk body weight is calculated by multiplying full body weight by 0.96.
Throughout this work, Megan and her graduate committee identified several areas where more data is needed. For example, information to quantify the effects of forage processing, cow body condition, milk yield and milk composition would further improve our ability to accurately estimate feed intake in a group of beef cows.
