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Daily Cattle INTRODUCTION The thermoneutral zones depicted in Figure 2 indicate that neonatal calves possess a wider range of temperature tolerance than either lambs or piglets. Adult cows are second only to sheep with full fleece with respect to thermal tolerance. That efficiency of performance of dairy cattle of all ages is influenced to an extent by both high- and low-temperature conditions is generally recog- nized. However, due to variability in systems of management employed on dairy farms, there is a tendency to only generalize on alterations in feeding to meet the nutritive requirements for maximum performance under hot or cold conditions. The major reasons are that dairy cattle are not usually fed for maximum growth rate or full genetic potential for milk production, and the management systems create either micro- or macroenvironments that affect maintenance needs of the animals. Dairy animals are generally kept: (1) on pasture with full exposure to the weather elements, (2) in drylot or pasture with access to tree shade or a constructed shelter free choice, or (3) confined within a barn or shelter with or without engineering inputs to control temper- ature. With few exceptions, dairy cattle will be subjected to all three systems during their life. Frequently they undergo exposure to two of the systems daily. Lack of environmental modifications to reduce the impact of the weather during either mid-summer or mid-winter may have both short- and long-range effects on energy needs for maintenance (R. E. McDowell, Cor- nell University, personal communication). For instance, maintenance needs 75
76 APPROACHES FOR PRACTICAL NUTRITIONAL MANAGEMENT on a daily basis may be 30 percent greater from about noon to 6 p.m. than for 2 to 10- a.m. Correspondingly, total daily requirements may -be 30 percent or more greater for the periods July-August and January-February than dur- ing other seasons. A lactation period frequently covers nearly the full range of the seasonal effects. The nutritive requirements are also confounded by stage of lactation effects on milk yield. THERMAL ZONES FOR DAIRY CATTLE Except for the neonatal calf, the estimated range of temperature for highest efficiency of energy utilization is about 13-18°C; however, significant changes in feed intake or in numerous physiological processes will not usu- ally occur within the range of 5-25°C (McDowell, 1972~. Above 25°C or be- low 5°C appetite will be influenced by the thermal environment (Figure 5~. The degree of this effect depends upon numerous factors, e.g., type of feed, quantity of feed offered, level of atmospheric humidity, length of pelage, and for lactating cows the stage of lactation and daily milk yield. From O to 60 days of lactation, appetite and feed intake are more affected by the ther- mal environment than in later stages of lactation (McDowell et al., 19761. Little is known about the relationship of potage to appetite or maintenance requirements in dairy cattle, but estimates indicate that growing longer hair during winter, shedding to short coat in summer, or even changing the posi- tion of the hairs from flat to erect can alter the rate of heat dissipation by a factor of three to five (McDowell, 19801. Wetting of the hair coat by snow or rain, wind speeds in excess of 6 km/in, relative humidity less than 30 or greater than 80 percent, or exposure to direct solar radiation in excess of 700 langley per day will also affect the rate of heat exchange and indirectly affect the critical temperatures. Some researchers have estimated important differences among European dairy breeds in lower critical temperature, e.g., Johnson and Ragsdale (1959) and Ragsdale et al. (1950), but in most of the studies the interaction effects of body weight, level of milk yield, and other factors have con- founded true estimates of breed effects. Since the thermoneutral zone is to a large extent controlled by the balance of heat production and rate of heat loss, numerous factors need consideration in ascertaining the best level of feeding for maximizing efficiency under various environmental situations.
Dairy Cattle FEED INTAKE AND ENERGY REQUIREMENTS DURING COLD STRESS Calves 77 Calves usually attain a reasonably stable body temperature within a few hours after birth (Williams, 19671; hence, they rapidly develop a rather wide tolerance to temperature (Figure 21. Elevated humidity levels in closed hous- ing for neonatal calves appear much more important than temperature to their well being. For example, Bates (1974) found lung damage in nearly all of 50 veal calves grown in individual metal stalls in a well insulated barn with tem- perature and humidity controls. Seldom are female dairy calves fed for maxi- mizing growth rate. Young calves (~30 days) are usually fed milk at the rate of 10 percent of body weight, and after a few days concentrates are of- fered free choice. It may be that additional milk feeding under cold condi- tions would stimulate gain, but this is expensive and increased risk of health disorders may arise (Hollon and Branton, 1970; McDowell and McDaniel, 1968). The recommended practices for feeding calves are projected to double birth weight by 3 months of age. Delay of doubling birth weight until 6 months will not deter attainment of normal size later; but when birth weight is not increased 100 percent by 8 to 9 months, there will be permanent ef- fects on both mature weight and skeletal size (McDowell, 19721. Calves that encounter a serious health problem, such as pneumonia, during the first 30 days of life are about three times more likely than normal calves to encounter a health problem later in life (Hollon and Branton, 1973; McDowell and Mc- Daniel, 19681. It appears, therefore, that level of feeding and care to ensure thriftiness in female dairy calves is more important than maximizing rate of growth. When male calves of dairy breeds are fed to maximize growth rate, the guidelines on requirements for various environments described for beef cattle appear appropriate. Heifers (6 Months to First Parturition) The normal management system for development of dairy heifers is to have them attain 50 percent of their expected mature size by 15 to 17 months of age and to reach 75-80 percent of expected mature weight at the time of first parturition, around 24 to 28 months. Since birth weight is ordinarily about 8 percent of mature weight, a modest rate of gain, approximately 0.5 kg/day, is required to reach 80 percent of mature weight and about 95 percent of ma- turity in skeletal dimensions by 28 months (Matthews et al., 1975~. Level of feeding needs adjustment to ensure sufficient energy to maintain normal heat balance during the various seasons. The exception would be the last 3
78 APPROACHES FOR PRACTICAL NUTRITIONAL MANAGEMENT months of pregnancy. Should this period coincide with mid-winter, it would be desirable to have about a 30 percent increase in energy intake to ensure a normal size fetus and some store of body fat (Williams, 19671. Lactating Cows The relative changes in maintenance requirements and dry matter intake for a 600-kg Holstein cow expected to produce 27 kg of milk with 3.7 percent fat content are shown in Figure 17 and tabulated in Table 21. The solid portion of the dry matter intake (DM) in Figure 17 was derived from a study of approximately 85,000 data sets of average daily yields of milk for 10-day periods under field conditions over a 12-year period when lactating Holsteins consumed a diet of alfalfa hay, corn silage, and concen- trates at a ratio of approximately 60 percent roughage and 40 percent concen- trates (McDowell, personal communication). The temperature-feed intake classes from 10~0°C were at 3°C intervals with the class limits set at a lower limit of 6 h above the class mean and not more than 12 h exceeding the class mean. When the hours for the class mean of temperature exceeded 12 h, the day was shifted to a higher class. For the low-temperature classes ~-10 to 20°C), a similar procedure was used to classify the days with a lower limit of at least 6 h per 24 h below the class mean and not exceeding 12 h. _ M ~D M oO 100 _ W_ ala ~ 50 _ Y ~ ,c Z ~ ca ~ 25 _ LU O , 1 1 1 -20 -10 Maintenance ~/20 R \60 R \ \ \ G R . 0 1 0 20 30 40 TEMPERATURE ( C) z LU 125 A: ° 3= uJ ~ ~ 3, UJ 100 zo adz c ~ in ~ E Z ~ - o FIGURE 17. Estimated maintenance requirements for a 600-kg cow over a temperature range of-15 to + 40°C; percentage changes intake of dry matter under low and high temperatures ex- pressed as percentage of level at 1 8-20°C for cows consuming ration of 60 percent roughage and 40 percent concentrates (60 R); and percent decline from 20°C for cows on 20 percent roughage, 80 percent concentrates (20 R) or on grazing alone (GR); "M" depicts estimated need at - 15 to -20°C with "B" indicating most likely intake level due to changes in behavior to conserve body heat.
Dairy Cattle 79 From-10 to 25°C there was a gradual decline in feed intake (Figure 171. Intake decreased rapidly when the daytime temperatures were 6 h or more above 30°C per day (60 R. Figure 174. The declines in feed intake at the ex- treme high and low temperatures were attributed to changes in animal behav- ior, i.e., standing to shiver in cold and resting to minimize heat production under thermal stress. At the very low temperatures, frozen silage influenced intake. The dashed line (M, Figure 17) is the estimated intake of the 60:40 ration at - IS to - 20°C, while "B" represents the more general pattern, i.e., a reduction in feed intake because of behavioral changes directed to- wards conservation of body heat and often less palatable feed. Using 18-20°C as a base point of 100 percent, intake increased with de- creasing temperature, reaching about lSO percent at -20°C. The estimated daily dry matter intake to maintain the 27-kg daily milk yield would increase from 18.2 kg to 21.3 kg (Table 21~. But because of the need to maintain heat balance, behavior (limited movement and shivering), coupled with usually lowered palatability of such feeds as frozen silage at-IS to - 20°C, the ex- pected dry matter intake will increase to only 20.4 kg per day. With rising TABLE 21 Relative Changes in Maintenance Requirements and Dry Matter for 600-kg Cows Producing 27-kg 3.7 Percent Fat Milk at Various Ambient Temperatures Along with Estimates of Actual Intakes of DM and Water Requirement for 27-kg Production Expectedc Temperature Maintenance DMb DM Intake Milk Water Intake (oc)a (% 18 - 20°C) (kg) (kg) (kg) (kg) - 20 151 21.3 20.4 20 51 - 15 133 20.2 20.0 23 55 - 10 126 19.8 19.8 25 58 - 5 118 19.3 19.3 27 63 0 110 18.8 18.8 27 64 5 103 18.4 18.4 27 67 10 100 18.2 18.2 27 67 15 100 18.2 18.2 27 67 20 100 18.2 18.2 27 68 25c 104 18.4 17.7 25 74 30 111 18.9 16.9 23 79 35 120 19.4 16.7 18 120 40 132 20.2 10.2 12 106 a Values for 25°C and higher temperature are for days with at least 6 h exceeding the tempera ture class but not more than 12 h. b Estimated requirements of DM intake for maintenance and 27-kg milk. c Estimates of intakes of DM and water and milk yield on water-free choice and ad libitum feed ing of ration of 60 percent hay and corn silage with 40 percent concentrates.
80 APPROACHES FOR PRACTICAL NUTRITIONAL MANAGEMENT maintenance requirements 20.4 kg or less intake will leave less ME available for milk synthesis resulting in approximately 20 kg of milk at-20°C instead of 27 kg (Table 211. Limitations on estimated water intake may also contrib- ute to the milk yield projected for - 20°C. From 10 to -10°C, cows will eat more to make up for an increased rate in heat loss, thus consumption of the 60:40 ration will rise provided additional feed is offered (McDowell et al., 19761. At -10 to - 15°C or lower, poorer . performance may be offset by increasing the proportion of concentrates in the ration or providing closed housing in order that the body heat from the cows will maintain the environmental temperature above -10°C. There are three options that may be utilized individually or in combination to reduce the environmental effects on ME intake: provide shelter or protec- tion for the cattle to at least partially alleviate the stress of extreme tempera- tures; increase the proportion of concentrates in the diet, e.g., 20 percent roughage-80 percent concentrate; or use a combination of the two measures. Shifting of the concentrate ratio will enable cows to maintain ME intake nearer the level required to maintain 600-kg body weight and 27-kg milk yield per day over a wider temperature range than on diets higher in rough- age content (Figure 17, 20 R). FEED INTAKE AND ENERGY REQUIREMENTS DURING HEAT STRESS Calves There are no data available at this time for recommending changes in calf feeding under hot conditions. As already indicated, researchers and dairymen have been more concerned with economics of feeds and thriftiness than in rapid growth for female calves. Heifers Above latitude 38°N in the United States, the birth weight for Holstein fe- males is in the range of 40~5 kg and they average 350 to 370 kg at 15-17 months (time of breeding), 45~500 kg at 2~26 months, and 600-640 kg at maturity (Matthews et al., 19751. At latitudes of less than 34°N in the United States and in the Caribbean region, Holstein females weigh 6 to 10 percent less at birth (38~1 kg) and average approximately 16 percent lower in weight at maturity (51~540 kg) than in the northern latitudes. These dif- ferences in weight occur even when the heifers are sired by the same bulls and quantity of feed is not limiting (Hollon and Branton, 1970; McDowell, 1972; Yazman et al., 19814. In these warm climate areas, daily maximum temperature exceeds the upper critical temperature of 27°C during 6 to 12
Dairy Cattle 81 months of the year. Exposure to heat stress will increase maintenance energy requirements for at least a portion of each day. Correspondingly, appetite is depressed, resulting in smaller fetuses and slower rate of growth after birth. As indicated previously, lower quality forages with reduced digestibility are no doubt an additional factor. It appears, therefore, that it could be prohibi- tively expensive to produce 600-kg or more Holsteins at maturity in warm climates. Seasonal changes in temperate areas will usually result in heifers calving from July to September being 3 to 4 percent lighter at time of parturi- tion than paternal half-sibs calving in January and February. Further evalua- tions of seasonal effects on the nutritive requirements for heifers is desirable. Lactating Cows According to the values in Figure 17 and Table 21, maintenance require- ments for a 600-kg Holstein will rise markedly when exposed for 6 h or more per day to temperatures above 30°C, a relative humidity of 70 percent or higher, and solar radiation exceeding 700 langleys per day. In order to main- tain an output of 27 kg of milk per day, dry matter intake should increase from 18.2 to 20.2 kg when temperature rises above 35°C. However, heat stress will suppress appetite (Figure 51; hence, reduced rather than increased feed intake must be accepted. At 35°C, dry matter consumption will be about 16.7 kg per day (Table 211. With reduced intake and increased maintenance needs, milk yield will decline by 33 percent at 35°C and by over 50 percent at 40°C. Water intake will be high at 35°C but will show some decline for most cows at 40°C due to a much lower dry matter intake. Increasing the proportion of concentrates in the ration will raise the upper critical temperature on intake (Figure 17), but in spite of type of feeding, in- take will decline. Efficiency of utilization of the feed may also decline. As rate of feed intake declines because of heat stress, the rate of rumen motility declines, which slows rate of passage. The data in Table 22 illustrate the im- pact of time of exposure to temperatures above 27°C on gross efficiency (kg milk/Meal NE) for Holsteins. Irrespective of stage of lactation, gross effi- ciency remained high with exposure to no more than 20 days of maximum temperature above 27°C. Up to 40 days exposure depressed efficiency signi- ficantly in the early and late stages of lactation. Cows exposed 40 to 87 days showed marked depression ~ - 27 percent) in efficiency from the cows ex- posed 20 days or less. The approximate range of correlations between climatic variables and daily milk yield under field conditions has been -0.35 to 0.30, with most from - 0. l to 0.2. The variance has ranged from 3 to lO percent, depending on stage of lactation, e.g., 14 percent for cows ~lOO days in lactation, 8 percent lOl-200 days, and lO percent 201-300 days (McDowell, 1974~.
82 APPROACHES FOR PRACTICAL NUTRITIONAL MANAGEMENT TABLE 22 Gross Efficiency (kg milk/Mcal/NE) for Holsteins in First Lactation When Maximum Daily Temperature Did Not Exceed 27°C or Exceeded 27°C 21 to 40 or 40 to 87 Days per 100 Days of Lactation Stage of Number of Days, Maximum > 27°C Lactation (days) O to 20 21 to 40 40 to 87 O to 100 0. 85a 0. 74b 0. 62C 101 to200 0.82 0.77 0.75 201 to300 0.87 0.78 0.72 Abe Values in the same row with a common superscript are not significantly different, but do dif- fer from those not having the same superscript (P < 0.05). SOURCE: McDowell et al., 1976. Correlations between ME intake and weather conditions have been highest for conditions occurring on the same day or one day previous, whereas milk yield was most highly correlated with EAT the preceding 2-5 days. Several experiments (Guthrie et al., 1968; Johnson et al., 1962; Maust et al., 1972; Razdan and Ray, 1968; Thomas and Razdan, 1973) showed that given the opportunity, cattle made a day-to-night shift in feeding during summer, e.g., 12.4 percent more DM consumed during the night while in winter cows ate 8.5 percent more DM during the day. In none of these experiments were there significant depressions in total daily DM intake or milk yield, even though daily maximum temperature exceeded 27°C. On farms near San Juan, P.R., a warm, humid area, Holsteins offered feed at the rate of 2.5 multiples of maintenance in ME averaged 16 kg milk per day. For 16 h the temperature exceeded 27°C with a low of 25°C, which permitted little opportunity for the animals to cool off (Table 231. When near the same level of ME was offered, Holsteins in New Iberia, La., also warm and humid in July, milk yield was 17 kg; 26 kg at Phoenix, Ariz., (hot, dry); and 23 kg at Ithaca, N.Y. The average mean daily temperature was 28°C in San Juan, New Iberia, and Phoenix (Table 23), but hours above 27°C ranged from 13 to 16. Although the Phoenix area cows were exposed to the highest temperatures, the low humidity and rapid cooling of the environment after sunset permitted restoration of heat balance and higher feed intake. The New York cows were exposed to the fewest hours above 27°C, but feed intake was markedly affected by high humidity and poor acclimatization to the heat stress due to only short periods of high temperatures. Environmental modifications, such as confined housing, can be utilized to modulate the nutritive requirements of lactating cows outside the TNZ. Con- fined housing has the advantage of reducing heat production resulting from
Dairy Cattle 83 TABLE 23 Average Hourly and Daily Temperature During the Month of July for Tropical (San Juan), Subtropical (New Iberia), Semiarid (Phoenix), and Temperate (Ithaca) Areas Hour San Juan, New Iberia, Phoenix, Ithaca, of Day Puerto Rico Louisiana Arizona New York 00 26 24 22 20 01 26 24 21 19 02 26 23 21 19 03 26 23 20 18 04 26 22 20 18 05 25 22 19 17 06 25 22 22 17 07 26 23 25 18 08 27 26 28 19 09 28 27 29 20 10 29 28 30 22 11 29 29 32 25 12 29 31 33 27 13 30 32 35 30 14 30 32 36 32 15 30 32 38 31 16 29 32 37 30 17 29 32 36 29 18 28 31 35 28 19 28 30 33 26 20 27 28 30 24 21 27 27 28 23 22 27 26 26 22 23 27 25 23 21 Daily average 28 28 28 23 walking to graze but there are limitations which must be kept in mind. For example, the humidity may rise above the critical level and foot problems from wet floors may offset the reduction in energy needs from walking and changing the thermal environment (McDowell, 19741. SUMMARY The feasibility both from the standpoint of economics and biological effi- ciency for supplying additional feed for higher maintenance needs of calves and heifers of dairy breeds under hot or cold conditions is not clear at this time. It seems that except under extreme circumstances for calves or heifers in later stages of pregnancy, added feed is not practical as compensatory gains in other periods will occur. The lactating cow producing over 6,000 kg
84 APPROACHES FOR PRACTICAL NUTRITIONAL MANAGEMENT of milk per lactation becomes the real target for adjustments in feeding, but here again practical solutions have limitations. As long as the kilogram of milk per megacalories of estimated net energy consumed exceeds 0.8, the of- fering of more feed will usually pay. This means it is practical to increase feeding when environmental temperature is below 0°C but of questionable value during mid-summer or in warm climate regions since the output of milk per megacalorie of energy may decline to 0.6 or less. Environmental modifications to alleviate or reduce the stress of cold or hot conditions offer promise as an alternative to higher intakes of ME but caution must be exercised to ensure the interaction effects are not negative. An addi- tional alternative to more feed or housing is to change the genotype of the an- imals. Heritability of feed efficiency appears greater than zero; estimates for dairy breeds range from 0.12 to 0.48, indicating genetic progress could be made in selection for increased gross feed efficiency (Freeman, 19751. Data for appropriate estimates on which to base selection are very costly to obtain. Milk yield and changes in body weight are joint responses to feed intake. These traits are correlated both phenotypically and genetically to feed effi- ciency- (phenotypic correlation fat corrected milk (FCM) yield and FCM per megacalorie estimated net energy - 0.82), thus yield and efficiency are not individually controlled by independent sets of genes. Researchers have, therefore, given emphasis to selection for total milk yield as the most practi- cal means of increasing gross efficiency. Use of breeds smaller than Holstein or cross-brads may give the appearance of improved efficiency under ex- treme thermal conditions; but when considered on the input-output ratio per unit of metabolic size, the validity of changing breeds to increase gross effi- ciency becomes less convincing. The general conclusion is that improved in- formation is needed to provide more accurate guidelines on feeding dairy cat- tle in various environments, particularly under field situations.