Protein meal toxicity
Protein meal toxicity in beef cattle can occur when certain protein-rich feed ingredients are consumed in excess or inappropriately. The term “protein meal” typically refers to concentrated protein supplements derived from plant or animal sources, such as soybean meal, cottonseed meal, sunflower meal, or other protein-rich feeds. While these protein meals are valuable sources of essential amino acids for cattle nutrition, improper usage can lead to toxicity issues.
Protein metabolism | Feeding strategy | Symptoms of toxicity | Treatment | Minimising risk of toxicity | Recommendation
Protein metabolism
A proportion of all protein is degraded to ammonia in the rumen and rumen microbes use ammonia as their source of nitrogen with digestible carbohydrate from feed for their growth. This process converts low quality roughages to microbial protein that the animal can use.
Excess ammonia passes into the blood stream and is converted to urea in the liver. The urea can then be excreted or recycled through the rumen. If ammonia levels get too high, the liver cannot convert it all to urea and toxic levels may be reached.
Although ammonia toxicity is generally a result of excessive urea intake, a similar result can occur with highly degradable protein meals if they are very palatable and eaten quickly in sufficient quantity (Table 1).
Some protein-rich plants used in meals may contain anti-nutritional factors or toxins. For example, certain oilseed meals may have compounds like gossypol in cottonseed meal, which, if consumed in large quantities, can be toxic.
| Table 1: Protein content and degradability of protein meals | ||
| Protein meal | Protein content* (%) | Rumen degradability |
| Canola meal | 38 | High |
| Copra meal | 15-20 | Low |
| Cottonseed meal | 38-43 | Medium |
| Palm Kernel meal | 15 | Low |
| Peanut meal | 46 | High |
| Soybean meal | 44-48 | High |
| Sunflower meal | 30-38 | High |
* Protein content on ‘as fed’ basis
Drought conditions increase the risk of ammonia toxicity because:
- The combination of poor quality forage and low intakes reduces the amount of carbohydrate available to rumen microbes and consequently their ability to utilise ammonia.
- The slower rate of digestion, which results from poor quality forage, provides more opportunity for proteins to degrade in the rumen and release ammonia.
Feeding strategy
Deaths in animals fed soybean meal indicate that offering two to four days intake at one feeding, as generally done with cottonseed meal and copra meal to reduce bullying, is hazardous. To date, no problems have been reported where the feeding methods restricts soybean meal intake i.e. fortified molasses, urea and salt dry licks or mixed with dicalcium phosphate.
Symptoms of toxicity
Predominately nervous signs have been observed. These may include:
- head tremor with side-to-side twitching
- weight shifted off front feet with circling on hind feet in the one spot
- tail flicking
- eyelid twitching
- high stepping in front
- apparent blindness
- slight bloating
- licking at flank
- depression
- sternal recumbency with death often occurring in this position.
Treatment
The antidote for ammonia toxicity (urea poisoning) is oral dosing with vinegar if treated in the early stages of poisoning. Dosage for cattle is 600ml; sheep 120ml diluted with water.
Minimising risk of toxicity
Recommendations to avoid potentially hazardous intakes are:
- do not offer more than one day’s intake at a feeding (Table 2)
- ensure there is adequate trough space (20cm/hd) so ‘bullies’ have less chance to over eat
- ensure animals have adequate roughage
- gradually introduce animals to highly palatable feeds. This is particularly important if animals have previously been fed less palatable feeds
- add products, which are known to control intakes in a particular area. Possibilities are salt and dicalcium phosphate or as a fortified molasses mix.
| Table 2: Recommended protein meal intakes for survival feeding | |
| Class of animal | Protein meal intake (kg/hd/dy) |
| Weaner | 0.5 |
| Lactating breeder | 1.0 |
All stock fed high protein rations following periods of poor quality feed, should be vaccinated to protect against enterotoxemia.
Recommendation
Closely monitor animals when introducing or changing to a high protein content meal, and contact the Customer Service Centre or your local veterinarian if sickness or deaths occur.