Nutritional challenges placed upon the lactating cow can be extreme in Arizona. One challenge placed upon the cow is the extra nutritional requirements caused by lactation. Figure 1 illustrates the weight loss which usually occurs in a lactating cow during the first 45 to 60 days of lactation. At the period of time at which the cow has lost the most weight, producers are trying to rebreed her in order to maintain a yearly calving interval. It is usually not possible to entirely prevent weight loss during early lactation with range cattle. A better strategy is to plan ahead to allow for weight loss by building or maintaining body fat stores before calving.
Another challenge with Arizona ranching opera- tions is the reduction in forage quality with mature forage. Rainfall often occurs in a biannual pattern and forage quality before the monsoon rains and in late winter can be low. As forage matures, protein, total digestible nutrients (TDN), and phosphorus often de- cline below levels considered adequate. In addition, certain trace minerals may be deficient year round. It is a good practice to analyze dormant forage to deter- mine protein, TDN, and phosphorus content. You can then match cowherd supplementation to the forage resource (Sprinkle, 1996a). It is also a good practice to analyze forage for trace mineral status over two or three years to establish baseline data for your ranch. Trace minerals in Arizona which may be of concern are selenium, copper, zinc, sulfur, and molybdenum.
There are several options one can take to help meet the nutritional challenges placed upon cows by lacta- tion and the environment. Some of the most prominent strategies are listed below and shall be explained more fully:
- Create a “fat storage cushion” for lactating cows by maintaining body condition score (1 to 9, 9 = fattest; Richards et al., 1986) at 5 or greater before calving. As part of this strategy, utilize protein supplements for low quality forage to increase forage intake and digestibility.
- If in spite of your best efforts, cattle are thin at breed- ing time, attempt to “flush” cattle with your best qual- ity pasture and/or by supplementation. If combined with short term calf removal, flushing will be more effective.
- Match calving season to the forage curve.
- Genetically match the cow to the environment.