Broodmare nutrition: Lactation remains most demanding period

Proper broodmare feeding is not much different than for any other female breeding animal. When it comes to nutrient needs for all young-bearing animals, the latter stage of pregnancy — especially lactation — is most demanding. What's most important prior to pregnancy is that the mare is neither too thrifty nor overweight, with a proper body condition score for her size (5-6, moderate to fleshy).

"Don't forget about your barren mares as the breeding season approaches," cautions Jim Brendemuehl, DVM, PhD, Dipl. ACT, assistant professor, University of Illinois College of Veterinary Medicine. If they are in an anabolic state coming into the breeding season, they will be more apt to be fertile/conceive.

As far as the non-pregnant mare is concerned, Brendemuehl explains, barren mares can be somewhat neglected, turned out to pasture and forgotten until the start of the breeding season. The result? Many will lose substantial body condition, stop cycling and won't start until they put the weight back on.

"I had a large number of underweight mares ship in the first of February this year, and they did not cycle for two months with body condition scores of about three, and ovaries the size of peas. It was not until they gained about 200 pounds, before they'd think about cycling," he adds.

Pregnancy

During early pregnancy, from conception through eight months, while food intake and body weight should be monitored carefully, classical thinking was that the mare did not need additional nutrition.

Burt Staniar, PhD assistant professor of equine nutrition, in Virginia Tech's Animal Sciences Department, reports that while the concept may be correct in regard to energy, it may not be so in regard to other nutrients.

"At this time we're just not sure," he says. To say that the fetus is not developing that fast during the first months of gestation is one thing, but whether there are nutrients — be it amino acids for tissue, minerals for proper cartilage and bone growth, or vitamins — that might be better at levels above maintenance prior to the latter stages of gestationis unknown.

Traditional thinking is that good-quality pasture alone or good-quality hay can easily sustain the horse. During the early portion of gestation, the mare should be fed at the maintenance level of 1Mcal/per lb. feed, which may be met solely by good pasture or forage, about 15 pounds for the average light mare (1,100-1,200 pounds), along with a trace-mineral salt block free choice. This should provide about 8% crude protein, 0.3% calcium (Ca), and 0.2% phosphorus (P).

"We observed that mares would gain a lot of weight during mid-gestation (2nd trimester), and that weight gain was fairly flat during latter gestation," says Laurie Lawrence, PhD, professor/equine nutritionist, Department of Animal Sciences, University of Kentucky.

Maybe naturally, mares were inclined to eat plenty when available to build up fat stores to be used during latter gestation. Many mares back off feed during later gestation, possibly due to the lack of room from the fetus.

"From an energy, and possibly protein standpoint, it may be important to consider a modest increase in energy/protein intake during the 2nd trimester, rather than trying to force the mare to consume more later in gestation, especially if you think her intake is going to be dropping off," Lawrence states. It may be better to feed a bit more early on. While the pregnant mare uses body fat stores for energy during pregnancy, she does not have similar reserves of protein.

If the mare is re-bred during foal heat she will need to be treated differently because of the combination of early lactation and early pregnancy. In this case, she will need not only increased energy intake, but also protein quantity and quality, especially lysine.

Mineral/vitamin nutrition are probably more important for pregnancy during early lactation, than for the foal she's nursing, who can get supplemental Ca-P from creep feed/pasture forage. Her milk, though, should adequately provide those nutrients for the foal because the mare's demand is to provide them to her developing fetus and to her milk. During early lactation, the foal's non-milk DM (dry matter) intake is relatively low, and therefore its needs come primarily from the milk.

Lawrence has been looking at markers of bone metabolism during late gestation and early lactation. From these serum markers, it appears that mares are mobilizing bone minerals during lactation, with these indicators elevated during this time. The indicators of bone mineral deposition are somewhat depressed in late gestation, as early as eight months.

"One of the issues is that with the commercial mare (one that is continually pregnant and re-bred) you have a very small window of opportunity, where she has stopped lactating, before fetal demands increase again," Lawrence explains.

If the mare at weaning is thought to be in a maintenance mode, she is really at about six months of gestation (if re-bred). Traditional thinking was that we don't have to worry about her until nine months. However, it is now thought that approach is possibly incorrect, and that we have to think about providing better nutrition during this time. If the mare has depleted her mineral stores, she's able to catch up easier if fed at a higher plane of nutrition earlier rather than solely in late gestation. This may not be of similar concern for the mare that has a foal every once in a while, but for those mares that are continually re-bred, this might be necessary. There may be cumulative effects on such continually bred mares. There is some data suggesting that bone strength in mares may be decreased with increasing parity.

"I'd be concerned about mares' exposure to endophyte-infected (E+) fescue toxicosis," says Brendemuehl. "Make sure that pregnant mares during late gestation are off fescue or management ensures that such mares are not under the influence of endophyte."

Open mares grazing E+ fescue can have a significant delay in initiation of cyclicity in the spring. The eropeptine alkaloids in E+ fescue depress prolactin, which normally increases in the spring in response to increasing day length. It is thought that prolactin has a stimulatory effect on follicular development. This effect can be reversed by the administration of dopamine antagonists like domperidone or sulpiride. The second area where E+ fescue has a negative effect on reproduction is during early gestation. Mares grazing E+ pasture have lower pregnancy rates and increased embryonic loss rates than mares grazing non-infected grass. Once the pregnancy reaches 30 days, the toxic effect is minimal and no greater losses are noted until foaling.

Once a mare reaches the latter stages of pregnancy, months nine to 11, then her needs change to ensure proper foal development. At that time a modest increase in energy content and protein concentration is best achieved by adding a bit of grain and maximizing protein using some alfalfa hay rather than solely timothy or other grass sources.

According to the NRC's Nutrient Requirement for Horses (1989, but soon to be revised), the mare requires 1.1 times her maintenance energy intake during her last trimester and a slight increase of crude protein (44g CP/Mcal DE) since greater than 60 percent of fetal growth occurs during the last 90 days of gestation.

Broodmares in late pregnancy, NRC states, "should be fed good-quality roughages, or a combination of roughages and concentrates in sufficient amounts to allow the mare to store body fat that can be utilized for energy needs during early lactation and rebreeding." The practitioner should remember that mares on substandard winter pasture need additional forage and probably a bit of grain, since the pasture is likely of lesser quality, and decreased environmental temperatures increase body-energy needs. Light breed mares can be fed about five to eight pounds of grain in addition to good quality forage.

As the pregnancy progresses, prior to parturition, the mare should be gaining weight (about 0.3 to 0.8 pounds per day). A mare needs to be of proper weight at foaling since she will tend to lose weight during lactation. Her peak milk production heightens nutrient needs and can consequently draw on body stores causing loss of body condition and weight loss, especially during the first two months. Some mares gain little or no weight during latter gestation, and deliver normal-size foals. Maintenance of conditioning helps to ensure conception at re-breeding.

"The mare can draw herself down a little bit and still have a healthy foal," states Paul Siciliano, PhD, a North Carolina State University associate professor of animal sciences.

"You want to make sure the mare is in adequate body condition throughout, though if you're not changing her diet, as she progresses into the latter stages of gestation, she may actually lose some weight," Siciliano says. When the additional feed required (i.e. energy/protein) from early to late gestation is determined, mares can fairly easily increase their intake to meet those needs on all-forage ration, if it is a good quality forage, along with a vitamin/mineral supplement.

"The other thing about open or early-gestation mares is not letting them get too thin during the winter," says Brendemuehl. If so, they may lose a lot of perineal fat. This is also true of mares during heavy lactation. Consequently their perineal conformation goes from acceptable, (i.e. not sunk-in, not aspirating air and fecal material) to the extreme (poor perineal conformation). The mare must have an effective conformational barrier to prevent fecal (bacterial) contamination from ascending the reproductive tract and causing an infection and/or abortion. If those mares lose excessive weight, they tend to get a big slope in a vulval shelf. Many of five-month to seven-month gestation/pregnancy losses can be associated with those mares whose conformation becomes poor and they suffer from fecal contamination. Vaginitis and/or placentitis occur, resulting in pregnancy loss/abortion.

Lactation

The mare's requirements significantly change during lactation, the most critical period for nutrient needs. During this period, she's recovering from the stress of parturition. She has to support her own body condition, while she literally pours herself into her developing foal. Mares will double their maintenance energy intake during lactation. She will easily increase her food intake, but poor-quality roughage and low-concentrate intake will not allow a mare to consume sufficient supply to meet her body's demands. To compensate, increased nutrient density and feeding sufficient grain is necessary. If her energy intake and nutrient makeup is insufficient, though her body weight and condition may decline, milk production and composition will not suffer, unless her intake is extremely deficient. The mare essentially sacrifices her own tissue stores to provide for adequate foal intake causing her to decrease body condition. To prevent this decrease, it is important to maximize energy — provide protein, calcium, phosphorus and increase the concentration of other essential trace nutrients to ensure those requirements are met. Enhanced energy and protein intake promote increased milk production.

During early lactation, the mare will produce milk at about 3 percent of her body weight. The average 1,200-pound mare will produce about 36 pounds of milk at this time, which is predominantly water. Practitioners should note that water is an essential nutrient and that water intake will increase during lactation, to about 20 to 24 gallons per day. Milk production normally peaks between 30 and 60 days, then steadily decreases. (After 90 days, mares cansolely provide nutrition for the foal. Creep feeding and pasture provides the difference.) While producing milk, the mare's total food intake is more than 2.5 percent of her body weight (a 1,200-pound mare will eat about 24 to 36 pounds of grain and forage daily), which should be higher in protein (12%), and in Ca (0.45%) and P (0.3%). Good quality legume hay should be supplemented with about 12 pounds of grain (~1 lb./100 lbs. BW/day).

During late pregnancy lactation, a mare needs at least 60 IUs of vitamin A per kilogram of body weight. If she's not on good grass pasture, she might need supplementation.

The mare's intake of the vitamin, primarily via grass pasture, is not vitamin A per se, but its precursor, beta-carotene. Along with its primary function as the major pro-vitamin A-source, beta-carotene is an antioxidant, which has been shown to be beneficial to reproduction. Once absorbed, it is found in abundance in the mare's colostrum and corpus luteum. It has been reported that beta-carotene supplementation produces earlier and stronger heats, improves conception rates, tends to reduce embryonic mortality and aids in maintenance of pregnancy.

It is beneficial to provide supplemental vitamin E (2,000-4,000 IUs per day, or >150 IU/kg feed) to breeding mares, especially those in confinement. Green pasture forages, high in vitamin E, are not always available to gestating and lactating mares that often foal during winter months.

It has been suggested (Harper, 2002) that mares known to have poor-quality colostrum, poor milkers, or those who have failed to passively transfer immunity in previous years, be supplemented with vitamin E at twice the required level for at least a month before and after foaling. It is also recommended that pregnant mares fed lower-quality hay or that graze endophyte-infected fescue be given vitamin E supplementation a month before and after foaling. It has been shown that mares supplemented with water-soluble natural vitamin E (1,500 IU d-alpha-tocopherol per day) for 21 days before foaling showed higher plasma alpha-tocopherol at foaling, as did their foals at 12 to 36 hours after birth. The higher-serum tocopherol levels in foals of supplemented mares is probably due to greater colostrum transfer. Natural-source water-soluble forms of vitamin E have shown greater bioavailability. Vitamin E supplemented-mares have shown increased passive transfer of antibodies to foals, which greatly enhances their immune system.

Serum and colostrum IgG levels were greater in mares supplemented with 160 IU of vitamin E per kilogram of feed (along with a mixed grass hay and grain ration), than those receiving 80 IU vitamin E per kg diet. The foals from all mares had similar levels of IgG, IgA, and IgM at birth. After nursing, foals from mares fed the higher level of vitamin E, had higher serum levels of IgG and IgA, which were reflected in their dam's colostrum.

As lactation subsides, the mare's feed intake, especially energy and protein content (grain) should be decreased gradually. If she's been re-bred, she's now about five months to six months pregnant and has to be fed accordingly. If not, her body weight should again return to proper barren weight.