HOW TO OBTAIN HIGH GROWTH PERFORMANCE IN DAIRY HEIFERS WITHOUT AFFECTING MAMMARY GLAND DEVELOPMENT

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1 HOW TO OBTAIN HIGH GROWTH PERFORMANCE IN DAIRY HEIFERS WITHOUT AFFECTING MAMMARY GLAND DEVELOPMENT Kristy M. Daniels Department of Dairy Science Virginia Tech Blacksburg, VA USA 2015 INTRODUCTION Dairy production in Brazil is important; milk ranks 5 th among all agricultural products in Brazil (FAO, 2012). In contrast to the United States, it is estimated that more than half of Brazil s milk for human consumption is supplied by small family farms (in Honorato et al., 2014). Further, most of the milk in Brazil is produced by crossbred cows (Holstein x Zebu) maintained primarily, but not always, in grazing production systems (Abdalla et al., 1999). From the author s perspective, there is tremendous potential for Brazilian dairy farmers to improve the production efficiency of dairy cows by making more informed management decisions. Challenges facing dairy farmers in Brazil, in no particular order, seem to be: mastitis prevention and treatment, milk quality, control of external and internal parasites, heat stress, managing breeding and genetics in order to find the right animals to fit the farmer s desired production scheme, and nutritional management. All of the factors listed above can either directly or indirectly affect mammary development and lactation performance. The focus of this treatise is on how nutrition can affect mammary gland growth and development. However, prior to discussing that, heat stress and genetics will be briefly addressed because they too can impact mammary growth and development. The management of heat stress and genetics are likely of equal or greater importance than nutritional management, in terms of affecting heifer mammary development in Brazil. HEAT STRESS AND MAMMARY GROWTH AND DEVELOPMENT In 2006 it was reported that for the US dairy industry, heat stress alone accounted for $900 million in economic losses (Collier et al.,

2 2-3 rd International Symposium of Dairy Cattle 2006). In mature cows it is known that heat stress changes nutrient needs of cattle. Because dry matter intake is typically reduced in cows during heat stress, increased diet nutrient density is suggested (increased grain or increased fat). Also, because a large amount of potassium is lost due to increased sweating, potassium requirements are estimated to be 12% higher in heat-stressed cows (Collier et al., 2006). Increased amounts of drinking water are also required by heatstressed cows. But what about heifers? How does heat stress affect them? Thermal status of dry cows alters fetal growth and postnatal calf development. Studies in this area are rare but it is guessed that more information will be available soon. Heat stress during gestation is associated with reduced placental (Collier et al., 1982, Bell et al., 1989) and birth weights of calves (Tao and Dahl, 2013). Reduced body weight growth rates may or may not extend postnatally (Tao and Dahl, 2013); more research is needed in this area. In this regard, it is feasible to speculate that mammary growth can be altered in utero by maternal heat stress with lifelong effects postnatally. Lastly on the topic of heat stress in heifers, maternal heat stress can influence immune function of the offspring. Passive transfer of immunity is negatively affected by maternal heat stress (Tao and Dahl, 2013). Poor passive transfer of immunity does not bode well for general calf health and growth; indirectly mammary growth could be affected by this. Recommendations: Monitor temperature humidity index (THI) onfarm, or at least periodically measure rectal temperatures (normal: 38 to 39.3 C) and respiratory rates (normal: 24 to 36 breaths per minute) of cattle. Assess provision of shade, fans, and sprinklers, access to water on your dairy, and ration formulation to minimize effects of heat stress on all animals, not just heifers. GENETICS AND MAMMARY GROWTH AND DEVELOPMENT To a large extent, a particular heifer s milk production potential is set by genetics. Bos indicus breeds of cattle and crossbreds are well adapted to grazing coarse pasture, enduring dry seasons, resisting parasites, and tolerating direct effects of climate; they are also known to have higher critical THI values for normothermia than bos taurus breeds (Madalena et al., 2012). The tradeoff for having the previously listed positive attributes is reduced genetic potential for milk production.

3 V Simpósio Nacional de Bovinocultura de Leite - 3 Simply put: cattle with bos indicus genetics are predisposed to lower milk production potential when compared to cattle with bos taurus genetics. Postnatal nutrition programs for heifers with bos indicus genetics that are aimed at improving mammary and somatic growth cannot exceed genetic potential for these things. Opportunities for improvement still exist though. Recommendations: As discussed in greater detail below, develop nutritional programs that will allow heifers, regardless of genetic background, to come closer to reaching their genetic potential for milk production. Focus on the nutrition of pre-weaned heifers first and then older heifers. NUTRITION AND MAMMARY GROWTH AND DEVELOPMENT About 15 years ago, scientists in the US revisited the study of nutritional effects on mammary development in pre-weaned heifers. The general consensus was that at this stage of life elevated nutrient intake may actually have positive effects on mammary development, much like what is seen with frame growth. As a result, the past decade has produced a great volume of experimental work focused on the nutritional management of pre-weaned heifers and measures of mammary growth and development, and unfortunately to a lesser extent - subsequent milk production. In the early 2000s, researchers at Michigan State University showed that increased energy and protein intakes commonly associated with accelerated calf growth programs increased growth of mammary parenchymal tissue (the epithelial portion of the gland that will one day secrete milk). If subsequent milk production had been measured in those animals there may have been increased milk production due to enhanced development of this tissue, but we have no way of knowing this. Nonetheless, studies such as this have painted a slightly different picture of the effects of nutrition on mammary growth and development in pre-weaned heifers. This period of growth seems to be a time when the udder is not adversely affected by level of nutrition; many signs actually seem to point toward a positive effect. Soberon and Van Amburgh (2013) recently published results of their meta-analysis. They compiled data from several studies that compared preweaning calf nutrition and future milk yield of the same animals. Eleven of the twelve original studies showed a positive relationship between nutrient intake and milk production, however, individually these studies lacked enough

4 4-3 rd International Symposium of Dairy Cattle animals to have sufficient statistical power that would allow the scientists to detect treatment differences (Soberon and Van Amburgh, 2013). When analyzed together via meta-analysis, Soberon and Van Amburgh (2013) were able to demonstrate statistical significance. They found that nutrient intake from milk or milk replacer during the preweaning period (first 2 mo of postnatal life for most US dairy calves) positively impacted long-term productivity (Soberon and Van Amburgh, 2013). Put another way, it was estimated that calves fed milk or milk replacer with growth rates of 0.60 to 0.80 kg/d before weaning produced 429 ± 106 kg more milk during first lactation compared with calves fed to gain 0.25 to 0.40 kg BW/d before weaning (Soberon and Van Amburgh, 2013). The biological basis for increased milk production is currently unknown but is likely linked to increased overall body protein accretion in early life. As mentioned before, the ultimate goal for those in this field is to find ways to rear heifers as efficiently as possible without negative consequences for milk yield potential in the herd; the preweaning period of life seems to be especially important for this. We also need to conduct more experiments that explore environmental as well as genetic factors that may affect growth and lifetime milk production potential. Lastly, we must remember that reduced calf growth, for any reason, will result in an unrealized increase in profitability due to unrealized milk and should be avoided. COMMENTS ON HEIFER NUTRITION AND BENCHMARKING In the author s opinion, most farms in Brazil are currently not in danger of overfeeding heifers. Underfeeding, or not feeding to the heifer s growth potential, is more likely the issue in Brazil. In Brazil, where cattle with high proportions of bos indicus genetics exist, age at first calving is variable and reportedly averages around 40 mo of age (Abeygunawarda and Dematawewa, 2004; Nogueira, 2004; Corrêa de Figueiredo Monteiro, 2014). Age at first calving in the USA is typically 24 mo of age (primarily Holstein genetics). This means that in Brazil, on average heifers are bred at 31 mo of age, compared to approximately 15 mo of age in the USA. This is a big difference! A younger age at first calving means a younger age at breeding, and younger age at puberty. How does attainment of puberty factor in to age at first calving?

5 V Simpósio Nacional de Bovinocultura de Leite - 5 Puberty is a biological threshold that is more associated with body weight than age. This means that heifer diet can be adjusted to support higher average daily body weight gains. This in turn allows the heifer to reach the goal of puberty at a lower age. It follows that the heifer on such a program will have an earlier age at first breeding, and lower age at fist calving. This situation occurred over the course of 30 years in the USA; age at first calving has decreased from 30 mo of age in 1982 to 24 mo of age presently. During this same span of time, body weight at puberty has remained unchanged and occurs at approximately 280 to 290 kg. In the US, the prepubertal ADG target for Holstein heifers is near 1 kg/d. This goal is routinely met by feeding high quality diets with high nutrient bioavailability. In Brazil, 1 kg/d ADG may seem infeasible, but it is biologically possible even in young calves, as demonstrated recently in crossbred (1/2 to ¾ Holstein x Gyr) bull calves (Silva et al., 2015). In that experiment, calves fed 8L of whole milk (25.6% CP, 28.5% fat on dry matter basis) per day with ad libitum access to a 19.5% CP (DM basis) starter averaged 886 grams of live weight gain per day over the course of 64d (Silva et al., 2015). A typical body weight at puberty in crossbred Brazilian dairy heifers is unknown to the author. However, assuming that bos indicus heifers achieve puberty at 60% of adult body weight (Abeygunawarda and Dematawewa, 2004) and a typical mature body weight is 480 kg (Rotta et al., 2015), then puberty is likely to occur at a bodyweight near 288 kg. This is almost identical to the puberty body weight threshold for US Holstein heifers. Figure 1 shows the effect that average daily gain can have on age at puberty. Heifers that continuously gain 1 kg/d from birth are likely to reach puberty at 251 d of age, compared to 502 d of age for a similar heifer on a diet that only supports 0.5 kg/g of body weight gain.

6 6-3 rd International Symposium of Dairy Cattle Figure 1 - Average daily gain can hasten or delay the time required to obtain a body weight associated with puberty. What Does it Take to Gain One Kilogram of Body Weight? In order for a calf to gain 1 kg of body weight per day, it must retain about 30 g of nitrogen on a daily basis (discussed in Davis and Drackley, 1998). Nitrogen retention values for dairy calves (as a percentage of total dietary N intake) seem to average about 47% and vary based on actual composition of the diet (Hill et al., 2008; Silva et al., 2015). Hill et al. (2008) reported N retention (as a percentage of total dietary N intake) across 4 diets to range from 44.7 to 65.1%, with a mean of 55%. In a Brazilian study that incorporated 6 dietary treatments, N retention ranged from 23.5 to 63.9% of total N intake, with an average of 42% (Silva et al., 2015). Neither of these experiments used foragebased feeds; all diets were concentrate-based and therefore quite readily digestible. Using the average N retention percentage across these two trials of 47% as an example - if the goal is for a calf to gain 1kg/d, it must retain 30 g of nitrogen, and therefore it must consume about 64 g of dietary nitrogen (30g / 64g =.47). Similarly, if the calf is to gain 0.5 kg/d, it must retain 15 g of nitrogen and must consume about 32 g of dietary nitrogen per day. If 6.25 is used as a conversion factor for nitrogen (ignoring the milk component in the diet for this part of the example), this means the calf diet should contain about 400 g of crude protein (6.25 x 64). For a calf gaining only 500 g/d, dietary crude protein should be about 200 g/d.

7 V Simpósio Nacional de Bovinocultura de Leite - 7 So, what does daily crude protein intake look like in practice and are the previous statements about crude protein intake and ADG supported by any recent data? The following examples are put forth to illustrate these points. Two studies are compared. The first study used uncastrated Holstein bull calves and was performed in the USA (Yohe et al., 2015) and the other study used crossbred (1/2 to ¾ Holstein x Gyr) bull calves and was performed in Brazil (Silva et al., 2015). These data are presented in efforts to demonstrate the importance of nutrition on body weight gains, especially lean tissue growth in the form of muscle. Earlier it was said that if the calf is to gain 0.5 kg/d, it must retain 15 g of nitrogen and must consume about 32 g of dietary nitrogen per day contained in 200 g of crude protein. Actual calf performance data from 2 separate trials show that this rough estimate is close, but far from perfect (Table 1). This is a very simple illustration and the reader is asked to keep in mind that in the USA, the apparently digestible protein (ADP) system is used to estimate the actual protein requirement of young preruminant calves (Table 1). Also, this illustration ignores the very important, perhaps even more limiting effect, of dietary fat on meeting overall energy requirements (Table 1). At any rate, farmers may wish to use the values listed on calf feed tags and/or raw milk composition values to help do this simple exercise on their own. If a desired rate of body weight gain is specified, are enough nutrients being fed to support this gain? Another way that this question might be asked is, if I feed my calves a 20% CP, 20% fat milk replacer along with starter, how much should I expect calves to gain?. This theoretical scenario is explored in Table 1; one might be surprised! To aid in calculations, milk replacer is typically 97% DM and starter is usually about 89% DM. Recommendations: Develop nutritional programs that will allow heifers to reach their genetic potential for growth and milk production. Focus on the nutrition of pre-weaned heifers first and then older heifers. In the USA a common goal is for calf birth weight to double in 60d. Consider using this benchmark in your calf program. Also consider how diet ingredients will affect allowable body weight gains of heifers and the overall profitability of the dairy farm. Remember that when feeding milk replacer that it is not typically a 100% substitute for whole milk; read the label carefully before using it to ensure that it will allow for the desired body weight gains in animals. Concentrate feedstuffs are generally more digestible than forages and calves eat them readily; (18% CP should be

8 8-3 rd International Symposium of Dairy Cattle considered a minimum level, 22% CP starters are common in the USA) allow calves access to concentrate feedstuffs and water from birth. Strive to maintain steady body weight gains throughout the weaning process and to puberty. Body weight gains of about 0.80 to 1.0 kd/d should not negatively affect mammary gland structure and will likely lower age at puberty, thereby allowing for earlier breeding and a lower age at first calving. The take home point of all of this is: calves need to be fed well if they have any hope of gaining body weight, reaching puberty, getting bred, calving, and becoming a productive member of the herd!

9 V Simpósio Nacional de Bovinocultura de Leite - 9 Table 1 - Calf average daily gain (ADG) is linked to dietary nitrogen (N) and crude protein (CP) content. Data from two research trials with bull calves and one theoretical scenario are presented. If a calf is to gain 0.5 kg/d, it must retain 15 g of nitrogen and must consume about 32 g of dietary nitrogen per day (47% N retention) contained in about 200 g of crude protein AVG g DM/d %CP, DM g CP/d g total CP N/d 1 intake, g/d total N intake, g/d birth weight, kg final weight, kg trial length, d Actual ADG, kg/d Energy allowable ADG, kg/d Yohe 2 milk replacer Starter Silva 3 (4L +S) whole milk Starter Silva 4 (8L +S) whole milk Starter :20 example 5 Milk replacer Starter * :20 example 6 Milk replacer Starter ADP allowable gain, kg/d 1 For milk and milk replacer: g of CP/ 6.38 = g of N. For starter: g of CP/6.25 = g of N.; 2 Yohe et al., 2015.See reference section. ; 3 Silva et al., Data from treatment 4L +S. See reference section.; 4 Silva et al., Data from treatment 8L +S. See reference section.; 5 This is a theoretical example that uses a 20%CP, 20% fat (asfed) milk replacer fed at 452 g/d of DM, with starter composition and intake similar to the 4L +S Silva example.; 6 This is a theoretical example that uses a 20%CP, 20% fat (as-fed) milk replacer fed at 452 g/d of DM, with starter composition and intake similar to the Yohe example.; *calculated as: 0.47 x 20.7 g N intake = 9.72 g N retained, which should support kg/d of ADG if it is known that 15g of retained N supports kg/d ADG.; Calcuated with Dairy NRC software (2001) for a 60 kg calf at 21 C. Whole milk, when used, was listed as 25.4%CP (DM), 30.8% fat (DM). All calf starter was considered to be 18%CP (DM) for these examples. A 22% CP (DM), 10%fat (DM) milk replacer was used when a milk replacer other than a 20:20 was desired.

10 10-3 rd International Symposium of Dairy Cattle REFERENCES ABDALLA, A. L., H. LOUVANDINI, I. C. S. BUENO, D. M. S. S. VITTI, C. F. MEIRELLES, AND S. M. GENNARI. Constraints to milk production in grazing dairy cows in Brazil and management strategies for improving their productivity. Prevent. Vet. Med. 38: ABEYGUNAWARDENA, H. AND C.M.B. Dematawewa Pre-pubertal and postpartum anestrus in tropical Zebu cattle. Animal Reproduction Science 82 83: BELL, A. W., B. W. MCBRIDE, R. SLEPETIS, R. J. EARLY, AND W. B. CURRIE Chronic heat stress and prenatal development in sheep: I. Conceptus growth and maternal plasma hormones and metabolites.j. Anim. Sci. 67: COLLIER, R. J., G. E. DAHL, AND M. J. VANBAALE Major advances associated with environmental effects on dairy cattle. J. Dairy Sci. 89: COLLIER, R. J., S. G. DOELGER, H. H. HEAD, W. W. THATCHER, AND C. J. WILCOX Effects of heat stress during pregnancy on maternal hormone concentrations, calf birth weight and postpartum milk yield of Holstein cows. J. Anim. Sci. 54: CORRÊA DE FIGUEIREDO MONTEIRO, C., A. APARECIDO SILVA DE MELO, M. ANDRADE FERREIRA, J. MAURICIO DE SOUZA CAMPOS, J. SENA RODRIGUES SOUZA, E. THUANNY DOS SANTOS SILVA, R. DE PAULA XAVIER DE ANDRADE, AND E. CORDEIRO DA SILVA Replacement of wheat bran with spineless cactus (Opuntia ficus indica Mill cv Gigante) and urea in the diets of Holstein x Gyr heifers. Trop. Anim. Health Prod. 46: DAVIS, C. AND J. DRACKLEY The Development, Nutrition, and Management of the Young Calf. Iowa State University Press. Ames, IA. FAO (Food and Agriculture Organization of the United Nations) Agriculture Data: FAOSTAT. Accessed Mar. 19, HILL, S. R., K. F. KNOWLTON, K. M. DANIELS, R. E. JAMES, R. E. PEARSON, A. V. CAPUCO, AND R. M. AKERS Effects of milk replacer composition on growth, body composition, and nutrient excretion in preweaned Holstein heifers. J. Dairy Sci. 91:

11 V Simpósio Nacional de Bovinocultura de Leite - 11 HONORATO, L. A., L. C. P. MACHADO FILHO, I. D. BARBOSA SILVEIRA, AND M. J. HÖTZEL Strategies used by dairy family farmers in the south of Brazil to comply with organic regulations. J. Dairy Sci. 97: MADALENA, F. E., M. G. C. D. PEIXOTO, AND J. GIBSON Dairy cattle genetics and its applications in Brazil. Livestock. Res. Rural Develop. 24(6)2012. NOGUEIRA, G. P Puberty in South American Bos indicus (Zebu) cattle. Animal Reproduction Science 82 83: ROTTA,P. P., S. C. VALADARES FILHO, T. R. S. GIONBELLI, L. F. COSTA E SILVA, T. E. ENGLE, M. I. MARCONDES, F. S. MACHADO, F. A. C. VILLADIEGO, AND L. H. R. SILVA Effects of day of gestation and feeding regimen in Holstein Gyr cows: I. Apparent total-tract digestibility, nitrogen balance, and fat deposition. J. Dairy Sci. 98: SILVA, A. L., M. I. MARCONDES, E. DETMANN, F. S. MACHADO, S. C. VALADARES FILHO, A. S. TRECE, AND J. DIJKSTRA Effects of raw milk and starter feed on intake and body composition of Holstein Gyr male calves up to 64 days of age. J. Dairy Sci. 98: SOBERSON, F. AND M. E. VAN AMBURGH Lactation Biology Symposium: The effect of nutrient intale from milk or milk replacer of preweaned dairy calves on lactation milk yield as adults: a meta-analysis of current data. J. Anim. Sci. 91: TAO, S. AND G. E. DAHL Invited review: Heat stress effects during late gestation on dry cows and their calves. J. Dairy Sci. 96: YOHE, T. T., K. M. O DIAM, AND K. M. DANIELS Growth, performance, rumen development and health characteristics of Holstein bull calves fed an Aspergillus oryzae fermentation extract. J. Dairy Sci. IN PRESS.

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