Beef production: Rearing systems and feeding

Beef is produced from dairy breeds and beef breeds, which can reside either in farms focused on dairy, beef or both.There are several options, which are all discussed in further detail.

Dairy breeds

Ayrshire calf

On a dairy farm the focus is on milk production. In the first option the farmer keeps only the dairy cows, heifers and calves which they will use for milk production. Less promising heifers and cows may be inseminated using beef breed semen to improve the carcass weight of their calves. Bull calves and other unwanted calves are sold to a calf rearing farm at the age of 1-8 weeks. Unwanted heifers and old or poorly producing cows are slaughtered.


On another rearing system calves are sold to the beef producer at a later stage, at the age of 2-3 months.

Some farms produce both milk and beef.  In this case all calves are reared on the farm until slaughter.  The farmer may buy more beef calves from surrounding farms. Dairy breed calves are kept for milk production, while beef breeds and less promising dairy breed animals are used in beef production.

Calves are most often reared using a three-phased method. The first phase is when the calf is born, and spends its first 10-26 days on the farm it was born in. Then it is sold to a rearing farm. The calves stay on the 2nd phase until their teens. The rearing time depends on the growth of the animals: in Northern Europe, the 2nd phase lasts 4-6 months. The farmer aims at daily growth of 900g and a mortality less than 4 %. The third phase is the finishing phase. Here the calf is reared until it's ready for slaughter. Finishing phase lasts 12-16 moths, and aims at animals weighing 350 kg. The animals are kept in groups in 15-30. When possible, each group is send to slaughter at the same time, and groups are kept steady to prevent fights.

Beef breeds

Ayrshire x Simmental -calf

Beef breeds are reared on a beef farms, which tend to be more extensive than dairy farms. Dairy animals are kept mainly indoors and fed heavily to promote milk production, while beef cattle is kept outside in paddocks. Feedlots especially in the Northern America are a concerning example of a production system, which is both extensive and intensive.

There are three types of beef production farms. Calf producers focus on keeping dams, who produce up to 10 calves during their lifetime. The calves are sold to a rearing farm, which is the second type of beef production. The third type is a combination farm, where the calves are bred and reared until slaughter.

Usually all breeding cattles, where the main target is to improve the genetics of the animals, are combination farms. In another option the calves are weaned and sold to a finishing phase farm. Here the animals are reared for 8-16 months, when they are sent to slaughter. The targeted live weight of animals depends on the breed, but ranges between 340-440 kg. The finishing phase farms usually accept only animals which are at least 75% beef breed.

Feeding

In beef production calves may be kept under their dams for 4-6 months, in which case weaning is a slow and natural process. If the calf is weaned from its mother sooner, usually during the first few days, one has to consider best methods for feeding the calf.

There are several options for feeding calves after the first few days of their lives, when they must be fed with colostrum.  Full milk is the most natural option, where calves get the milk which cannot be sent to the dairy. Liquid feeds are another option. the digestive tract of calves under 2-4 weeks of age does not secrete amylase, pepsin or rennin enough to be able to utilize vegetable fats or vegetable proteins. They can only utilize milk protein (casein), lactose and fats. After 4 weeks the calf
Their feed must have casein or whey protein and animal based fats. Water, hay and concentrated feed should be freely available at all times to support to development of the digestive tract.

Calves can be fully weaned from milk once they ingest at least 1 kg of silage a day. This happens usually at the age of 8 months, when the size of the rumen has changed from 30 % to 70 %, and in proportion the omasum and abomasum have shrunk from 70% to 30 %.

Distribution of energy from feed.

Growing cattle need energy, proteins, fat and water to maintenance and to production (see the picture on the left). The energy need for maintenance is measured as a BMR, basal metabolic rate. It includes the energy need for

• breathing
• blood circulation
• molecular synthesis to balance natural catabolism of tissues
• moving and using substrates in cells
• contraction of muscle cells, transfer of nerve impulses
• maintaining body temperature

Factors affecting the energy need for BMR are age, gender, breed, earlier energy status (prolonged malnutrition decreases BMR) and physiological status (is the animal for example in gestation or suckling its offspring). BMR is measured either direcly with a calorimeter or indirectly in a respiration chamber by calculating how much oxygen the animal uses, and much nitrogen and carbon dioxide it produces. The amounts of gases (liters / day) are then inserted to the Brouwer equation:

16,18 * O2 +5,16 * CO2 - 2,42 * CH4 - 5,90 * N in urine (g/day)

For growth, beef breed bulls need on average 10-27 MJ energy / day. A small bull growing 1 kg a day needs 10-15 MJ, while a bull putting on 1,5 kg a day needs 18-27 MJ a day and over 200 grams of protein a day. Castrated bulls (oxes) and heifers utilize energy less efficiently than bulls, and tend to grow slower and have a larger fat percentage than intact bulls.

Protein

Cattle get protein from two sources: from feed protein which has passed the rumen, and from rumen microbes. Both types of protein are metabolized in and absorbed from the small intestine. Therefore the animal's need for protein can be expressed as a need for protein absorbed from the small intestine. Another measurement is the protein balance of the rumen, which measures the amount of protein in the feed compared to the microbe's ability to utilize it. If the balance is negative, the microbes do not get enough protein from the feed. In a positive balance the microbes can utilize only a portion of the proteins, and often proteins pass through to the faeces. The balance is not calculated for animals weighing over 200 kg, for their rumen microbes are developed well-enough to withstand even a slightly negative balance.

The metabolization and utilization of protein is described in the picture below. Protein is originally acquired from feed. Undegraded protein, or unmetabolizable protein, is passes through the rumen to the small intestine, where a portion of it is metabolized and absorbed. The rest is exreted as faeces. Metabolizable protein is used by the rumen microbes, which in turn die and are passed to the small intestine. Major part of the amino acids in the microbes are metabolized, absorbed and used as tissue protein (or milk, if the animal is lactating).

The metabolization of protein in the digestive tract of a cattle. Original source unknown.

Sources for information on feeding: 

ARC1980. Agricultural Research Council. 1980. The nutrient requirements of ruminant livestock, technical review.

AFRC1990. Agricultural and Food Research Council. 1990. AFRC Technical Committee on Responses to Nutrients , Report Number 5, Nutritive Requirements of Ruminant Animal : Energy. Nutr . Abstr . Rev.(Series B): 60: 729 - 804

Dryden , G. McL . 2008. Animal Nutrition Science. www.gabi.org

Animal digestion

Monogastric animals

The digestive tract of an monogastric animal (animal with only one stomach) aims at breaking down the eaten feed, splitting the compounds into nutrients, transform them into usable form and excrete the non-digestable matter as feces or urine. This is achieved with digestive enzymes and/or microbes in the digestive tract.

Picture from lecture materials,
original source unknown

Digestion has roughly three phases: chewing or mincing, digestion and absorption. After absorption it is a matter of other tissues to use the nutrients for various chemical processes. The first phase, chewing, begins as the animal picks the feed to its mouth. Chewing adds the surface area of the feed, making it easier for enzymes to attach to it. Chewing also adds the excretion of saliva, which lubricates the feed and the esophagus. Saliva includes also growth factors, which support the renewal of the digestive tract epitelium. In some species, excluding ruminants, have amylase in their saliva, which breaks starch and glycogen into smaller polysaccharides. Mouth area has also several lymp nodules, which act as a first barrier against any bacteria in the feed.

Swallowing takes the feed in small chunks to the esophagus and down to the stomach. The stomach consists of four areas: cardia, fundus, corpus and pylorus. All areas have a different structure of mucous membrane: for example, cardia excretes mucus, but fundus excrete gastric juices. Pylorus has sensory nerves, which regulate digestion. Gastric juices include HCl, a strong acid, which lowers the pH of the stomach to 1-3 and this assists the denaturation of proteins and kills bacteria. Pepsinogen is secreted by the glands in the stomach, and transformed to pepsin by the HCl. Pepsin breaks proteins to small polypeptides. In addition to HCl and pepsinogen, the gastric juice includes water, inorganic salts and mucus.
In the stomach the HCl and pepsin are mixed with the feed as the stomach wall contracts, and the food mass becomes softer, warmer and more watery.

Pyloric sphincter acts as a gate between the stomach and the small intestine. The beginning of the small intestine is called duodenum. Pancreatic juices, intestinal gland liquids, bile and bile salts are all excreted to duodenum, where the feed mass is quickly neutralized (remember it's pH was about 1-3). Intestinal glands secrete a basic liquid which neutralizes the chyme (= food mass). Bile and bile salts from the liver mix water into fats, forming fat droplets. Lipase from the pancreas is actived by bile salts, and then it breaks the fat droplets into glycerol and fatty acids. Pancreas excrete also insulin and glucagon, which are used to transfer glucose from the blood into cells (insulin) or discharge stored glycogen into the blood as glucose (glucagon).

The next part of the small intestine is called jejunum. This is where most of the nutrients are absorbed, after they have been broken down to usable compounds in the duodenum. Pancreatic amylases break down polysaccharides into disaccharides, and disaccharidases into monosaccharides. Trypsin and chymotrypsin (from the pancreas) break polypeptides into smaller pieces, which are split into amino acids by peptidases:

Picture from lecture materials, original source unknown

From the small intestine the chyme moves to the large intestine, where microbes ferment it. Only water, electrolytes and volatile fatty acids (ruminants only) are absorbed from the large intestine. In addition, some B vitamins are formed in the large intestine.

Ruminants

The  saliva of ruminants doesn't have any amylase. Instead, it is rich in mucin, phosphates and carbonates, which balance the pH of the rumen. The esophagus differs from that of the monogastric animals in that it has two kinds of contractions: peristaltic, which move the feed pieces down to the rumen, and antiperistaltic, which bring boluses back to the mouth for the animal to ruminate. 

Ruminants have four stomachs, and only the last of them (the abomasum) functions like the stomach of monogastric animals. Ruminants have three fore-stomachs: rumen, reticulum and omasum. These are sites for microbial fermentation. Rumen is the first of the fore-stomachs, and in cows it can store up to 80 liters of feed. It hosts about 10¹¹-10¹² microbes / g of feed. The rumen contracts in three stages every 50-70 seconds. The contractions mix the feed (mixing the microbes into the contents of the rumen), releases methane as burps and brings boluses back to the mouth for the animal to ruminate. Rumen and reticulum are often considered as one, and called reticulorumen. The pH in the reticulorumen must stay between 5-8 for the microbes to work, and the gases must be let out as burps. Otherwise the rumen contractions are hindered and the animal may suffocate, as the methane fills the rumen and the lungs no longer have space to expand.

From the reticulorumen, water, Na, Cl, ammonium and water are absorbed. Omasum is the last of the fore-stomachs. It is filled with leafs, which sieve the feed, and prevent too large particles from reaching abomasum. From the omasum, water, minerals, ammonium and VFA are absorbed.

The final stomach for ruminants is the abomasum. It secretes pepsin and HCl, which lower its pH to 3-4. There the dead microbes from the rumen are digested enzymatically, and the proteins and fats in the microbes can be absorbed. Some of the proteins in the feed are not absorbed until in the abomasum. Abomasum also finalizes the digestion and absorption of other particles, which may not have been fermented in the fore-stomachs.