Dairy cattle basics: Part 3

To keep the rumen of a dairy cow healthy and functioning normally, make sure that her daily diet includes at least 35% roughage.

Dairy cows are ruminants, and thus have a unique digestive system that can utilise forage, such as hay, silage, pastures or straw, as well as concentrated feeds, such as grains or protein sources (fishmeal, cottonseed oilcake meal, or soya bean meal, for example). The ruminant stomach consists of four compartments: the rumen, reticulum, omasum and abomasum.

The rumen, which comprises about 80% of the stomach, has a capacity of about 160ℓ. It is basically a large fermentation vat and contains billions of bacteria, protozoa and fungi. These micro-organisms thrive in the anaerobic (containing no oxygen) environment of the rumen, where they digest and ferment the feed swallowed by the animal.

A mat of recently consumed, coarse feed floats on the surface of the contents of the rumen ( see illustration). The efficiency of rumen fermentation depends on the presence and maintenance of this mat, which traps the fine feed particles and provides shelter for the vast number of micro-organisms in the rumen.

Cows chew their feed into smaller portions while mixing it with saliva. They then swallow this mixture, which is known as a bolus. The longer pieces of feed are trapped in the upper layer of the rumen mat, while the smaller parts sink down into the lower part of the rumen fluid.

CONCENTRATES CAN BE MIXED AND FED SEPARATELY, OR MIXED WITH ROUGHAGE

The rumen contracts rhythmically two to three times a minute, and this moves the longer particles of feed to the back of the rumen and down into the reticulum, the second chamber of the stomach.

The reticulum initiates the regurgitating action, bringing coarse feed back into the mouth to be chewed once more. (The word ‘ruminant’ comes from the Latin ruminare, which means ‘to chew again’.)

water intake is less when she consumes a high-moisture feed.

All feeds contain moisture and dry matter (DM). Even dry feeds, such as hay or straw, contain between 8% and 10% moisture. Silages and pastures contain 65% to 85% moisture respectively. The DM content of the feed contains crude protein, energy, minerals and vitamins, which the cow utilises to produce milk.

The daily feed intake of a Jersey cow is between 14kg and 16kg DM, while a Holstein cow typically consumes 24kg to 28kg DM.

MILK YIELD

Most types of roughages on their own do not contain enough feedstuffs to maintain high milk yield level or growth. For this reason, you should give your cows concentrated feeds, such as grains and protein sources, as well. Concentrates can be mixed and fed separately to the

status just before irrigating and again the following day. This will enable you to see how far the moisture has penetrated. Remember, nitrogen is conveyed by the water in the soil, and any that leaches below the root system is out of reach.

MISINTERPRETATION

With drip irrigation, it is easy to over-irrigate if you use the wetted soil surface as a guide.

Drip irrigation wets an onionshaped pattern in the soil, so by the time the surface looks irrigated, you may well have grossly over-irrigated the plant. Be extra vigilant to avoid making this mistake.

When there is a chance of rain and you have to irrigate, apply light irrigations more frequently to reduce the chance of leaching when rain falls.

• Bill Kerr is a vegetable specialist and breeder. Email him at farmersweekly@caxton.co.za. Subject line: Vegetable production.

BILL KERR