Energy Value of Field Peas in Lamb Finishing Diets

Adapted from Hettinger Sheep Day Report, 1999, Erik Loe, Marc Bauer, Greg Lardy, Dan Schimek, Paul Berg, Berg Moore, NDSU

Acres planted to field peas in North Dakota have dramatically increased from 14,545 acres in 1994 to 102,849 acres in 1997. With the increased availability of field peas for use in livestock rations, there is a need to understand how field peas compare to other traditionally used feedstuffs in North Dakota.

The objective of this experiment was to evaluate the energy content of field peas in lamb finishing diets.

One hundred sheep were allotted to 20 pens in a randomized complete block design. Four diets were fed where peas replaced corn at 0, 15, 30, or 45% of the diet. The diet contained 75% dry rolled corn or peas, 10% alfalfa hay, 5% de-sugared molasses (CSB), and 10% supplement. Diets (Table 1) contained a minimum of 15% crude protein, .70% calcium, .36% phosphorus, 1.22% potassium, 1.74 Ca:P and 25 g lasalocid/T. Diets contained .20% blood meal and .80% feather meal to ensure that metabolizable protein did not limit gain. Diets also contained 6.0% soybean meal, .50% ammonium chloride and .19% urea. Vitamins and minerals were included to meet or exceed NRC recommendations. Sheep were blocked by weight and sex and allotted randomly to one of four treatments (5 pens/treatment).

Initial and final weights were an average of two consecutive day weights. Performance measurements included average daily gain (ADG), dry matter intake (DMI), and feed/gain (F/G). The lambs were slaughtered on August 18. Due to the selection of ewe lambs for replacement ewes, only carcass data from the ram lambs were collected. Ram lambs (3 pens/treatment) were slaughtered on day 89. Carcass characteristics included hot carcass weight (HCW), leg score, conformation score, flank streaking, marbling, color score, ribeye area (REA), fat thickness, body wall thickness, yield grade, and dressing percentage.

All lambs were used in the evaluation of performance measurements (Table 2). DMI had a cubic response (P = .02) where there was an increase in DMI from the 0% field pea diet (3.50 lb/d) to the 15% field pea diet (3.64 lb/d) and then a decrease for the 30% field pea diet (3.42 lb/d). All other performance characteristics were not affected by treatment (P > .14). Only ram lambs were used in the evaluation of carcass characteristics (Table 3). Flank streaking responded quadratically (P = .10). There were no other carcass characteristics affected by treatment (P > .18).

Based on lamb performance, there was a linear increase (P = .10) in dietary NEm and NEg as percentage of field peas in the diet increased (Table 4). The calculated NEm and NEg of field peas were 116 Mcal/cwt and 83 Mcal/cwt, respectively. Field peas have an NEg 24% greater than that of corn (83 vs 67 Mcal/cwt) when fed to feedlot lambs.

Table 1. Diet composition and nutrient composition*

Table 2. Effects of field pea on feedlot performance.

Table 3. Effects of field pea on carcass characteristics.

Table 4. Effects of field peas on dietary NE_m and NE_g.

Grass Tetany

Adapted from Guyer et. al, 1984

Grass tetany is a nutritional or metabolic disorder characterized by low blood magnesium; yet it is not just a simple magnesium deficiency. It is also called grass staggers, wheat pasture poisoning and hypomagnesemia. It primarily affects older cows nursing calves under 8 weeks of age, but may also occur in young or dry cows and growing calves. It happens most frequently when cattle are grazing lush, immature grass, but occasionally occurs when cattle are fed dry forages (winter tetany).

High potassium and nitrogen content of grass seems to be associated with low blood magnesium. High nitrogen fertilization seems to reduce magnesium availability, especially on soils high in potassium or aluminum. Grass tetany occurs most frequently in the spring, often following a cool period (temps 45 to 60°F) when grass is growing rapidly, but also is seen in the fall with new growth of cool season grass or wheat pastures.

Low blood magnesium may be caused by a diet low in magnesium; a diet with nutrient imbalances that interfere with magnesium metabolism; or higher levels of milk production. When blood magnesium drops too low, proper nerve impulse transmission fails, causing tetany.

The following have been observed in cattle with tetany: grazing away from the herd, irritability, muscular twitching in the flank, wide?eyed and staring, muscular incoordination, staggering, collapse, thrashing, head thrown back, coma, and death. Animals on pasture are often found dead without observation of illness. Generally, thrashing will be apparent if grass tetany is the cause of death.

The prevention of grass tetany depends largely on avoiding conditions that bring it on:

1. Hold cattle off new grass until it is 4 to 6" tall.
2. Feed dry hay or grain until grass provides adequate nutrition.
3. Maintain cows on a moderate plane of nutrition until ample grass is available.
4. If possible, feed some legume hay or graze early legume pasture, since legumes are higher in magnesium than grasses.
5. Feed a high magnesium mineral supplement.

In areas where tetany frequently occurs, feed cows supplemental magnesium. Supplementation increases blood magnesium levels and alleviates much of the grass tetany problem. Magnesium should be consumed on a daily basis.

Magnesium oxide is one of the better and cheaper sources of magnesium. Since it contains 54 to 60% magnesium, the rate of feeding magnesium is about .04 to .08 lbs per head daily. Palatability of magnesium is low; consequently, it should be included in a readily acceptable protein or mineral supplement.

Salt?mineral mixes can be satisfactory carriers for magnesium when consumption of salt is managed to regulate intake. Feed no other salt when using the mix as a magnesium carrier. Salt content and palatability of the magnesium?mineral mix can be adjusted to assure adequate intake by adding grain, molasses, soybean meal or cottonseed meal.

When feeding free choice mixes, whether commercial or home mixed, check to see that cattle are consuming the desired amount. If not, modify the supplement to increase or decrease intake by increasing or decreasing: 1) palatability, 2) the number of locations that the mineral is fed, or 3) the amount of salt or magnesium oxide in the mix.

Salt?mineral mixes should contain 10 to 15% magnesium. Range cubes should contain 2.25 to 4.5% magnesium when fed at the rate of 1 lb per head daily.

For commercial mineral supplements guaranteeing a minimum percentage of magnesium, you can calculate daily magnesium intake as follows: lbs intake daily x 454 (grams per pound) x percentage magnesium. For example, 100 cows consuming 140 lbs per week of a salt?mineral mixture containing 15% magnesium would consume approximately 13.6 grams of magnesium per head per day (140 lbs ¸ 100 cows ¸ 7 x 454 grams/lb x .15 = 13.6 grams/day).

The table shows some mixtures that may be suitable for preventing grass tetany. For each mix, adjust salt and/or the number of mineral feeders to maintain about 25 to 27 lbs of magnesium oxide per 100 cows per week.

Cattle afflicted with grass tetany need immediate treatment. Consult your local veterinarian regarding recommended procedures.

Decreasing losses from grass tetany depends on using one or more of the suggested preventative management practices and timely treatment of affected animals.

Most feed companies offer a high magnesium mineral mix for use on pastures which are prone to grass tetany or for use at times when grass tetany is likely to occur. You can also create your own mix using one of the following formulations.