Dairying in the Tropics: A Fight Against Weather and Low-Quality Feed

Editor’s Note: The following article was written by Elmer Edgardo Corea, faculty member in animal science at the University of El Salvador in El Salvador, who is a visiting Fulbright scholar sponsored by Jud Heinrichs, professor of dairy and animal science. His project is “Diet Evaluation to Reduce Nutrient Waste and Increase Feed Efficiency and Productivity in Cattle to Con-tribute to Food Security in El Salvador.”

In every area of the developing world, producing food to feed people is an essential issue. In Central American countries, dairy farms face the challenge of being productive despite some very adverse conditions. Holstein cows have evolved in temperate climates where they are best able to express their genetic potential to produce milk. However when these animals are exposed to an adverse environment such as in the tropics, their performance is limited in terms of reproductive efficiency and milk production.

Reproductive efficiency

Reproductive efficiency can be measured through such indicators as conception rate and days open. We realized that even the anoestrous period of cows (measured by milk progesterone) is no longer than 40 to 50 days on average; cows have low conception rates (<30%) and most often require 3 or more services to conceive. Milk production rarely exceeds 55 lbs/day in the most productive groups. Both reproduction and milk yield are affected by weather and feeding.

The farms that are close to sea level have the most severe conditions. With one dry and one rainy season, each lasting about 6 months, daily temperatures do not vary much throughout the year, but moisture varies considerably. Southern Central America experiences a slightly cool, dry period from November to February and a warm, wet period from June to September. It is known that a combination of humidity and temperature determines the intensity of heat stress on cows. These conditions influence to a great extent the cow´s ability to become pregnant. As a result of these severe weather conditions, a seasonal pattern is observed with most calving occurring in the last three months of the year. This results in more milk being produced from fresh cows in the more comfortable weather during the first months of the year.

Seasonal milk yield

The seasonality of milk yield is also influenced by the fact that heat stress limits the capability of cows to obtain peak milk levels as most often observed in fresh cows. These fresh cows have lower feed efficiency than they could have on fresh dry weather, again due to the heat stress. Also there is a marked increase in feet and mastitis problems resulting from wet, muddy conditions, which further inhibits milk production. The use of fans and sprinklers to cool cows helps to mitigate heat stress, but does not control these problems completely.

Forage crops

Feeding is often considered the main factor affecting animal performance. Cows in the tropics should eat half or more of their diet as forage as they do in other areas of the world. Most forage crops grow more rapidly with high temperatures and sunshine; however, this can drastically affect forage quality. Tropical forages, including grasses and crops such as sorghum and corn, often have higher fiber content and lower digestibility than normally desired for use in lactating cow diets. We have found that the neutral detergent fiber (NDF) content is often more than 65% in our tropical forages. Harvesting these crops for silage is not always performed at the proper stage of maturity due to problems with bad weather or other factors.

Hot and dry weather can also have negative effects on forage yield and quality since these conditions decrease dry matter yield while increasing NDF. When these very poor forages are used to formulate a lactating cow diet, their low protein and energy along with limited intake capacity by the cow make it a challenge to meet the animal’s nutrient requirements for high production.

We attempt to meet this challenge by including grain in a similar manner as is done in the Northeast. In many cases in Central America, milk production is influenced by the price and availability of grain, leading farms to have narrow economic margins in the worst months.

There is not much that can be done with regard to high temperature and humidity except to establish cooling systems or improve those not functioning well. In the case of feeding cows in the tropics, improving forage quality will have a significant impact on dairy farm profitability. Some alternatives that can be considered by Central American farmers are:

• To give attention to crop conditions and plant maturity at harvest. Crops should be managed for high yields but also for good nutritional value, which includes selection of appropriate varieties, fertilization, and pest control. Proper harvesting plays a key role in obtaining higher energy and digestibility of the forage; this may allow the cow to support better performance under adverse conditions.
• To complement forage with the addition of legumes to help obtain higher protein content and less fiber in the diet. Also, inclusion of legume forages in diets up to half of the forage dry matter often decreases the cost for the same nutrient content and increases milk yield with no effect on milk components.
  
• To analyze diet components for protein and fiber. Most problems with improper feeding come from the lack of knowledge of nutritional value of feedstuffs and the overestimation of them. This is especially important in the case of forage. Knowing fiber levels will allow farmers and nutritionists to have a good indicator of the energy value of the forage.
  

Some specialists believe that intensive dairy farming is not feasible in adverse conditions like those in the tropics. However, based on our experience we can show that some important key factors can be better managed to improve milk production and reproduction parameters. There is still much opportunity to improve dairy farming in the tropics by means of knowledge transfer and technology adoption. Improving forage management and cow comfort are two large parts that can improve our conditions.