Body Energy Management
Department of Animal Science, Michigan State University, East Lansing, MI 48824-1225 U.S.A.
# Take Home Messages
To very loosely paraphrase the First Law of Thermodynamics, Aif a cow begins lactation with the proper amount of body energy reserves, these reserves can be transformed from one form to another to help maximize milk production; but, from lactation to lactation, body energy reserves can not be destroyed, but must be replenished and maintained@. In other words, the cow must have an adequate reserve of body energy at the beginning of each lactation and she must be able to consume the balance of her energy needs as dietary energy in order to meet her biological potential for milk production, and the demands for reproduction, growth, and maintenance.
A successful next lactation starts with appropriate body energy management and feeding of pregnant cows beginning in the previous lactation, through the dry period. Proper management of cows through this transition has profound benefits on subsequent health, lactational and reproductive performance, and profitability.
Nutritionally, the main objectives in the prepartum period are to prevent energy and nutrient deficiencies or excesses which can lead to health problems, and to prepare the rumen ecosystem for the energy- and nutrient-dense diet in early lactation (1, 5, 16, 17, 18). Perhaps, the most important concept to appreciate is that cows from about 100 d before dry-off through early lactation progress through four physiological states --- lactating and pregnant; dry and pregnant; parturition; and, lactating and nonpregnant. Moreover, each physiological state requires different energy and nutrient management to prepare cows for the next state. Others have provided comprehensive information about nutrient management through transition (24, 25, 26, 44).
Cows in early lactation reach peak milk production before peak dry matter intake (DMI). This results in temporary negative energy balance and cows rely on body reserves to meet additional energy needs. Each kg of body fat can supply enough energy to produce about 7 kg of milk (45). Also, each additional kg of milk production attained between 4 and 8 wk of lactation (peak milk yield) can result in about 90 kg additional milk yield in that lactation (9). Therefore, ability to mobilize and utilize body energy reserves in early lactation is important to maximize total lactational performance.
The purpose of this paper is to review and discuss research work and concepts for optimal body energy and nutrition management of dry pregnant, fresh and early lactation dairy cows. This is especially important given the importance of this time period in setting the stage and outcome for the ensuing lactation. For this paper, the subject matter is organized into two time periods --- the time period preceding parturition and the period of early lactation. General topics addressed include: 1) overall energy status; 2) causes and prevention of ketosis; 3) key nutritional and diet considerations; and, 4) effects of fat supplementation in early lactation on reproductive function.
# Time Period Preceding Parturition
Body Energy Reserves and Body Condition
There is an old German adage which says, AThe eye of the master fattens his cattle.@ Building adequate body reserves before calving is crucial to optimize milk production, reproduction, and health in the next lactation. A system (1 to 5 scale) to assign body condition scores (BCS) was developed for use throughout the lactation cycle (70). Based on various performance responses, recommended BCS range from as low as 2.0 in early lactation (near peak milk yield) to as high as 3.75 for the dry period and calving (32, 50, 62,70).
Waltner et al. (67) published prediction equations relating BCS at calving with 90-d milk production. Highest 90-d milk yield was achieved when BCS at calving was between 3.0 and 4.0, regardless of lactation number. Also, greatest production of fat-corrected milk (FCM) in 305 d was associated with a decrease in BCS from calving to 120 d in milk of 0.5 to 1.0. Emery (18) reported that cows with BCS 4.0 or less had fewer incidences of health problems during the first 75 d of lactation compared with cows with BCS greater than 4.0. Braun et al. (8) noted that cows with BCS of 3.0 at calving had the highest average mature equivalent milk yield, whereas cows with BCS of 4.5 had the lowest. To achieve maximum peak milk yield and total lactation production, proper body condition at calving is paramount.
Doubtless, management of body energy of dairy cows through successive lactations is extremely important to their lifetime productivity. Though subjective, measurement and assessment of BCS and its changes at key points through the lactation cycle are a practical and useful way to manage body energy status. Body condition score as a proxy for body fat reserves relates well enough with the potential energy available for milk production to be used practically and successfully in modern dairy herds (10).
Under-conditioning. Low milk yield in the next lactation can be due to inadequate body reserves of cows fed to requirement or under-fed in the dry period. Cows fed to requirement (48) or under-fed during the dry period had lower average BCS (3.19 and 3.26) at calving compared with cows that were fed above requirement (3.97) (7). Cows fed above requirement during the dry period had similar dry matter intake (DMI) and greater milk yields compared with cows fed to requirement or under-fed. Similarly, if cows were under-conditioned at dry-off, increasing BCS in the dry period increased milk yield in the first 120 d of lactation (14).
Doubtless, in high producing herds and for high yielding cows special attention must be given to body energy management and energy provision. Cows administered bST (100 or 150 mg/cow per wk) and yielding more milk than controls, reached the dry period and calving with lower BCS than control cows (12). Also, cows which yielded more milk in the previous lactation had greater feed intake during the dry period probably as a result of lower BCS at dry-off, indicating that in this case extra energy provision during the dry period was needed to restore body energy reserves. Similar responses would be expected to occur in the dry period for cows with high yields even if not given bST, if sufficient replenishment of body reserves did not occur before dry-off. Cows must be able to replenish the previous drain on body reserves if they are to perform optimally in the next lactation --- consistent with the First Law of Thermodynamics.
Over-conditioning. Over-conditioned cows with BCS > 4.0 at dry-off had greater risk of reproductive and lameness problems in the following lactation (23). Emery (18) reported that dry cows with BCS >3.6 consumed 30% less feed during the 4 wk dry period than cows with BCS <3.6. Increased incidence of ketosis and abomasal displacement were associated with increased BCS in 1566 dry cows in 100 farms in Michigan (16). Higher prepartum (d 17) BCS was correlated negatively with DMI 21 d postpartum (26). If cows reach the dry period over-conditioned, they should not be forced to lose body condition because restricted feed intake and forced weight loss in the dry period predispose them to periparturient disorders (73). In the trial of Domecq et al. (14), over-conditioning at dry-off was associated with decreased milk yield in the first 120 d of lactation. Cows should not reach the dry period in excessive body condition (BCS > 4.0).
Ketosis and Fatty Liver
Negative energy balance and associated excessive body lipid mobilization can occur in periparturient cows leading to ketosis, increased blood non-esterified fatty acid (NEFA) concentrations, and increased hepatic triglyceride accumulation (29). These metabolic problems have negative impacts on subsequent lactational performance. Recent research shows promise for treatment of these disorders.
Propylene glycol. Using propylene glycol (PG) as a potential preventive treatment for ketosis and fatty liver has been studied (25, 59). Propylene glycol is converted to glucose by the liver which increases insulin concentration in blood (25). Increased insulin response reduces fatty acid mobilization from adipose tissue (6). Multiparous cows drenched once daily with 1 L of PG from approximately 10 d prepartum had greater plasma glucose and insulin, and lower NEFA concentrations from 7 to 1 d prepartum (65). Cows drenched with PG prepartum had reduced hepatic triglyceride accumulation at 1 and 21 d postpartum, and tended to have lower blood NEFA.
Also, increased glucose and insulin, and decreased β-hydroxybutyrate and NEFA concentrations in blood were observed in restricted-fed (50% of ad lib) pregnant Holstein heifers drenched with PG compared with no PG (28). Because drenching cows with PG is very labor intensive (25), delivering PG as a drench, in a grain mix, or in a TMR in restricted fed (50% of ad lib) non-lactating pregnant cows were compared (11). Delivery of PG in a small amount of grain was more effective than in a TMR to increase serum glucose and insulin, and reduce NEFA concentrations. Pulsing PG as a bolus, either as a drench or in a small amount of feed (e.g., concentrate or supplement) appears important to achieve the desired metabolic effects.
Formigoni et al. (22) fed 300 g of PG in a TMR from 10 d prepartum to parturition and then the same amount in a drench at 0, 3, 6, 9 and 12 d after parturition. Propylene glycol had no effect on milk yield or composition during the first 90 d of lactation, but lower plasma NEFA and higher plasma cholesterol concentrations were observed in PG-supplemented cows after parturition. At d 40 postpartum, 80% of the cows remained anestrus in both groups; however, by 90 d postpartum 58% of unsupplemented cows were anestrus, whereas only 30% of cows given PG were acyclic. Use of PG in early lactation may have some benefits on reproductive performance besides preventing fatty liver and ketosis.
# Early Lactation
Body Energy Status
Some body energy loss occurs naturally in early lactation. However, too much loss is a concern. Braun et al. (8) suggested that the goal was to maintain a BCS of 2.5 or greater in early lactation. Cows with BCS of 4.0 at calving had greater infiltration of fat in liver at 1 and 4 wk after calving than cows with BCS of 2.5 (52) and had lower DMI and milk yield in early lactation than cows with BCS of 2.5 (66).
Feeding Management and Nutrition in Early Lactation
Lack of acceleration of DMI early postpartum is one of the major factors limiting energy intake and peak milk production. Maximizing DMI in early lactation may help reduce body condition loss and incidence of metabolic disorders associated with negative energy balance (16), and accelerate milk yield to peak production.
Dry matter intake during the first week of lactation is 30 to 35% below peak DMI reached 8 to 10 wk postpartum (38). The rate of ascent of DMI depends upon many physiological and environmental factors which can be addressed through proper management and nutritional stratagems.
Maintaining normal ruminal function and optimizing microbial protein yield is essential to maximize milk production. Fresh cows need to consume rations with highly fermentable feedstuffs and high energy densities without upsetting ruminal microbial growth and fermentation.
Carbohydrates. Diets too high in fermentable carbohydrates reduce ruminal pH and DMI and predispose cows to ruminal acidosis and laminitis (1). On the other hand, rations too high in NDF limit DMI (43). Rations for fresh cows should contain 28 to 30% NDF and 21% ADF, dry basis (35). For cows in early lactation, rations should contain about 25% NDF and 19% ADF (47). Non-fiber carbohydrates (NFC) should comprise 38 and 40% of rations for fresh (0 to 3 wk of lactation) and early lactation cows, respectively. These diets should contain energy densities ranging from 1.67 Mcal NEL/kg for fresh cows to 1.72 to 1.74 Mcal NEL/kg for cows approaching peak production. Muller (46) recommended that diets for fresh cows contain higher concentrations of effective-fiber to minimize digestive problems. However, NDF, ADF and NFC concentrations do not account for variations in ruminal digestibilities or rates of degradation of either fiber or NFC (2).
Changing the rates of ruminal fermentation may not affect recommended dietary NDF, ADF and NFC contents, but can affect ruminal microbial metabolism and yield (2). For maximum DMI, cows in early lactation should be fed the highest quality forages possible, which are more fermentable (60). Also, the choice of forage in early lactation can reduce the time cows are in negative energy balance (68). Forage sources that reduce the time in negative energy balance were, from shortest to longest, corn silage, alfalfa hay and grass hay.
In addition to high quality forages, several by-products may benefit early lactation cows (49). The NDF digerstibilities of soy hulls, beet pulp and whole cottonseed are higher than those of most forages. Therefore, rations can be formulated using some by-products to maintain sufficient NDF concentrations and increase utilization of the fiber; thus, increasing energy intake. It is still paramount to have adequate effective-fiber from forages to promote normal salivary flow and ruminal function (1).
Supplemental Fat. Typical fat supplements are oilseeds (whole cottonseeds, soybeans, canola, etc.), animal fats (tallow or grease), prilled fatty acids and granular fats. Supplementing rations with roasted soybeans, extruded soybeans, or sunflower seeds and feeding 6% total fat in the ration DM increased milk production (40, 56). Milk production also increased when rations were supplemented with 2 to 2.5% tallow, prilled fatty acids or Ca salts of fatty acids (CaSFA) (29, 30, 71, 72). Granular fat supplementation increased milk production in some studies (20, 39, 57, 54); however, Scott et al. (58) reported responses varied according to total dietary fat concentration, BCS at calving, and genetic potential for milk production of the cows.
When to Start Feeding Fat. Responses to supplemental prilled fat in early lactation were not observed until 5 to 6 wk after supplementation, and the lag-time was attributed to reduced feed intake during the early lactation period (31, 33, 37). If supplementation with tallow was delayed until 5 to 7 wk postpartum, milk production and persistency of production were improved (27, 55). In contrast, Holter and Hayes (34) reported no difference in DMI or milk yield when CaSFA were fed beginning from d 1, 29 or 57 to d 112 postpartum. Overall, the literature indicates that supplementation of fat in early lactation can be delayed until 5 to 6 wk postpartum; however, practical application of this scheme may be difficult because of the variation in days in milk of cows within an early lactation group.
Niacin and Energy Utilization. Niacin is involved in energy metabolism (15). Ruminal microbes normally synthesize 2 to 3 times the amount of niacin typically supplemented (6 to 12 g/ cow per d). Overall, milk yield and milk composition responses to supplemental niacin were small in 29 study comparisons (19).
However, amount synthesized may be limited in early lactation when ration changes occur (36). Cows fed 6 g niacin/cow per d, 2 wk prepartum through 12 wk of lactation, produced more milk than unsupplemented controls (3). In another study during the same period of the lactation cycle, milk yield and DMI were not improved with 12 g/cow per d compared with no supplementation. However, plasma NEFA concentrations were lower with niacin compared with no niacin in warm weather, but not in cool weather in Wisconsin (61). However in Erdman's (19) summary, milk yield the first 15 wk of lactation only increased 0.41kg /cow per d with niacin, and milk composition was similar with or without supplementation.
Very high doses of niacin (120 g/ cow per day) were effective in prevention and treatment of ketosis (69). Supplemental niacin was hypothesized to be efficacious especially for over-conditioned cows expected to rapidly mobilize body lipid reserves in the peripartum period. However, results are inconsistent, and in a large field study thinner cows actually responded more favorably to niacin than fatter cows (4).
Practically, identifying the physiological and dietary situations when fresh cows might benefit from niacin supplementation is not well-defined. Considering the cost of niacin supplementation and the uncertainty of realizing a favorable response, the expected marginal return from feeding niacin would be slight in most cases.
Energy and Reproductive Function in Early Lactation
One of the major causes of infertility is an extended period of anestrus following calving; anestrus cows can not become pregnant. This may be a disadvantage in early lactation because early heats --- before negative energy balance becomes a problem --- are the most fertile. One study found that cows that did not ovulate before 30 d postpartum required more services per conception and were more likely to be culled nonpregnant than cows that cycled within the first 30 d of lactation (42).
Uterine Involution. Involution is the return of the uterus to normal location, size, and symmetry after parturition. Involution of the uterus can be influenced by many factors in early lactation. Abnormal calving and postpartum complications, such as milk fever and (or) RFM, have the greatest effects to reduce involution. Retained fetal membranes cause reduced uterine motility which impairs the elimination of fluids and reduction of uterine size. With each subsequent calving, involution becomes slower; age is not necessarily a factor. Moderate to severe negative energy balance, milk fever and even subclinical hypocalcemia can result in delayed involution (53).
Ovarian Function. Lactation and negative energy balance are major influences on number of days to first ovulation (42). Lactating cows produce larger follicles that are subject to slower turnover; thus, they may be more likely to become cystic. Negative energy balance has detrimental effects on both the follicle and the corpus luteum (CL). Inadequate energy intake results in reduced luteinizing hormone (LH) secretion. Because LH is responsible for stimulating follicular growth, reduction in LH results in smaller follicles. Ovulatory-sized follicles do not develop, and ovulation does not occur. As energy intake increases and negative energy balance subsides, LH secretion begins to increase. Greater LH concentrations in blood result in follicles that grow to maturity and ovulate. However, carryover effects of negative energy balance may last into lactation, reducing fertility even after the cow is in positive energy balance (42).
Reproductive function of cows with severe negative energy balance also is compromised by reduced CL function. The CL of cows in negative energy balance produce less progesterone and the effects of this are observed later in lactation. Progesterone concentrations are similar at first ovulation for cows with different degrees of negative energy balance. Second and third ovulations have reduced progesterone concentrations associated with them. Effects of negative energy balance on reproductive function in lactation can take 40 to 60 d to manifest in reduced pregnancy rates (42).
Excessive body condition loss during early lactation also can affect reproduction. Perkins et al. (51) categorized cows according to condition loss into minor (< 0.4 units), moderate (0.5 to 1.0 units) and severe (>1.0 units loss). Cows in the different condition loss categories had different BCS prepartum: minor = 3.7; moderate = 4.1; and, severe = 4.5. Cows in the severe group had lower DMI than those in the moderate or minor groups. Intervals from calving to first ovulation, first heat and conception were longer, and conception rate was lower for cows in the severe group.
Domecq et al. (13) noted that in a high producing herd in Michigan BCS at calving or at first artificial insemination (FAI) was not related with conception; however, dramatic loss of BCS between calving and FAI apparently had a negative effect on conception.
Supplemental Fat and Reproduction. Adding fat to diets increases energy density and may reduce negative energy balance. Feeding fat to cows in negative energy balance may shorten the interval to first ovulation. Dietary fat will increase the number of follicles produced and improve CL function. Adding dietary CaSFA increased size of the largest follicles which may cause over-secretion of estrogen, which can impair gamete transport, embryonic development, and (or) establishment of pregnancy (42). However, this appears to be a result of the CaSFA and not increased intake of energy per se (41).
Staples et al. (64) reported increasing fat supplementation had a positive effect on reproductive performance. Positive responses included greater plasma concentrations of progesterone, increased size of the ovulatory follicle, increased numbers of ovarian follicles, modulated regression of the CL and improved conception and pregnancy rates. Progesterone is required to establish and maintain pregnancy and the CL is a major source of progesterone (21). Plasma cholesterol, a precursor for the synthesis of progesterone during early lactation increased when supplemental fat was fed, which may be sufficient to improve conception (64). Increased progesterone may improve embryo survival and polyunsaturated fatty acids may reduce secretion of prostaglandin PGF2α which can contribute to maintenance of the CL and pregnancy (63).
Proceedings of the 1998
Western Canadian Dairy Seminar, Red Deer, Alberta
Volume 10 http://www.afns.ualberta.ca/wcds/wcd98/ch23.htm