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J. Dairy Sci. 88:154-158
© American Dairy Science Association, 2005.

Effects of Birth Date and Order in Lactation Performance of Iberian Red Deer (Cervus elaphus hispanicus)

T. Landete-Castillejos1,2,3, A. García1,2,3, J. A. Gomez2, M. I. Berruga2 and L. Gallego2

1 Instituto de Investigación en Recursos Cinegéticos (IREC, CSIC-UCLM-JCCM), Sec. Albacete (IDR),
2 Departamento de Ciencia y Tecnología Agroforestal, ETSIA, and
3 Sección de Recursos Cinegéticos, IDR, Universidad de Castilla-La Mancha, 02071 Albacete, Spain

Corresponding author: T. Landete-Castillejos; e-mail: tomas.landete{at}uclm.es.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ACKNOWLEDGEMENTS
 REFERENCES
 
This study discriminated between 2 effects (birth date and presence of older calves) assessed jointly in previous studies. Birth date delay produced similar effects to those reported previously: reduced milk and milk nutrient production in late-calving hinds, concentration of milk, substitution of protein by fat, greater body weight losses of dams (hinds), and reduced calf growth. Hinds in a group consisting of early- and late-born calves produced more milk, and calves grew more than their isolated counterparts. Evidence exists for consequences of foster suckling by early-born calves in mixed groups of early- and late-born calves at the end of the standard birth period, because these calves grew more than predicted by the milk production of their dams. In contrast, no detrimental effect was found in late-born calves of this group. Lack of differences might be due to the excess of hind milk production during the first 5 wk of lactation previously recorded in other experiments.

Key Words: red deer • lactation • milk composition • birth date

Abbreviation key: BD = birth date delay with respect to first calf born, TFY = total fat yield, TLY = total lactose yield, TMY = total milk yield during an 18-wk lactation, TPY = total protein yield


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ACKNOWLEDGEMENTS
 REFERENCES
 
Red deer is a seasonal breeder and most births occur within 1 mo (Kelly et al., 1987). However, a small fraction of births occur naturally in red deer and other cervids in the second or third month of the calving season (4.5% in red deer, Kelly and Drew, 1976; 11% in fallow deer, Dama dama, Birgersson and Ekvall, 1997). In an earlier study, we found that hinds calving late naturally produced less, but more concentrated, milk (Landete-Castillejos et al., 2000b, 2001). Milk hinds substitute protein (most directly related to growth) for fat and they lose more BW than hinds calving early (Landete-Castillejos et al., 2000b). Milk nutrient production also is smaller in late-calving hinds, and thus, their calves grew less than those born early (Landete-Castillejos et al., 2001). Similar, but less clear results have been reported when studying enforced 5-mo delays in calving (Landete-Castillejos et al., 2004a). The reason for this seasonal effect is not clear, but cervids, like cattle, humans, and most other mammals, produce milk mainly from nutrients ingested daily rather than from body reserves, as occurs in pinnipeds (Sadleir, 1987). Body fat can also be mobilized to support lactation during nutrient deficiencies (White, 1992; Landete-Castillejos et al., 2003a). Thus, because of a mid-late summer-associated reduction in voluntary feed intake (Kay, 1979, 1987; Kelly et al., 1987), late calving may result in fewer nutrients being available to support milk secretion.

In addition to the effect of birth date on milk production and calf gains, cross-suckling occurs, aimed preferentially at late-calving hinds by older calves (Landete-Castillejos et al., 2000a). These calves ingest more milk after wk 6 than that produced by their own dams, whereas these dams produce more milk than their calves can ingest from 0 to 5 wk of age. Such milk production excesses ensure sufficient milk for calf needs and likely reduce calf mortality during early lactation that results from milk thefts. This concept is supported by a positive correlation between early calf mortality and milk production excess (Landete-Castillejos et al., 2000a). However, in the cited study, both seasonal and milk theft preferentially by older calves are confounding effects mixed in the same experiment.

The present experiment was designed to discern between these 2 effects by comparing isolated groups calving early and late with a mixed group consisting of hinds and their calves of both age groups.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 ACKNOWLEDGEMENTS
 REFERENCES
 
Subjects were 49 Iberian red deer hinds and their calves (27 males and 22 females) kept in a 15,000-m2 open-front enclosure on irrigated pasture including 52.4% tall fescue (Festuca arundinacea), 28.6% cocksfoot (Dactylis glomerata), 14.3% Lucerne (Medicago sativa), and 4.8% white clover (Trifolium repens). During gestation and throughout lactation, hinds were fed ad libitum with diets based on suggestions by Brelerut et al. (1990), using barley straw, barley hay, alfalfa, oats, and sweet beetroot (16% CP). Although calves had access to feed, they were not observed to consume diets intended for their dams during the experiment. Individual feed intake of dams was not monitored.

Hinds were assigned to each of 3 groups kept in sections of the above enclosure roughly proportional to the group size. The first group consisted of hinds having standard birth dates (9 hinds having 5 male and 4 female calves; calving between April 25 and June 13, mean ± SE: May 19 ± 5 d). The second group consisted of hinds having delayed birth dates (15 hinds with 6 males and 9 female calves; calving between July 19 and September 8; mean ± SE: August 11 ± 4 d). The third group consisted of a mixture of hinds with standard (9 hinds having 5 males and 4 female calves; calving between May 8 and June 6; mean ± SE: May 24 ± 3d) and delayed birth dates (16 hinds having 11 males and 5 females calves; calving between July 19 and September 6: mean ± SE: August 10 ± 4 d). Birth date delay was achieved by allowing the females to mate at scheduled times. Iberian deer are seasonal polyestrous breeders and more than 50% of the females cycle between September and March (García et al., 2002). Birth date delay was defined as a delay in days from the first-born calf. Births were classified as standard (<50 d) or delayed (>80 d), with no births from 43 to 86 d.

Milk yield of hinds was assessed by milking. In deer, milk production has been assessed often by the double-weighing technique (Arman et al., 1974; Loudon et al. 1983; García et al., 1999), and less often by milking (Arman et al., 1974; Krzywinski et al., 1980). Results from double weighing are more variable than milking (Landete-Castillejos et al. 2000a), and they measure different processes. Double weighing estimates milk intake, whereas milking estimates actual milk yield. Milking was conducted on wk 2, 3, 4, and 6, and then every 4 wk to wk 18. Hinds were isolated from calves for 6 h with no preisolation milking for ethical reasons explained in Landete-Castillejos et al. (2000a). Individuals were milked under anesthesia (xylazine at 0.5 mg/ kg of body mass; ketamine at 1 mg/kg; reverted with yohimbine at 0.25 mg/kg of body mass) using a machine milking set up to 50:50 massage:milking ratio and 44 kPa of vacuum. Milk production and composition were assessed as described previously (Landete-Castillejos et al., 2000b, 2001).

Statistical Analyses
The ANOVA tested differences among the 4 groups (standard calving date in isolation, standard calving date of the mixed group, late calving date in isolation, and late calving date in the mixed group). Included in the ANOVA were factors that could influence subsequent lactation variables such as calf birth weight and hind BW.

The GLM procedure (Statgraphics, Manugistics, Rockville, MD) was used to examine milk production [total milk production (TMY), total protein production (TPY), total fat production (TFY), and total lactose production (TLY)], milk composition (percentages of protein, fat, lactose, and protein to fat ratio), calf growth, and maternal changes in BW between parturition and weaning. The models examined the effect of birth date delay as a continuous variable (BD) indicating the delay in days from the birth of the first calf born in the study. Because some effects may be produced by discrete seasonal physiological changes differing between standard and out of season lactations, birth date was also examined using a categorical variable, birth season [coded as standard (BD<50 d) birth dates = 0, and delayed (BD>80 d) birth dates = 1]. The effect of maintaining deer in groups of similar calf age (either standard or delayed) or calves widely differing in birth dates within the same year was examined by a categorical variable indicating whether there was a mixture of calf age in the group (coded as 1), or not having such mixture as in the group of standard birth date or delayed birth date (coded as 0). To discern birth date and mixture of calf age effects from other confounding effects, the model also included calf birth weight, hind BW after calving, sex of calf (male = 1 and female =2), and 2-way interactions. To prevent multicollinearity problems with related variables (BD vs. birth season, calf vs. hind BW), variance inflation factors (VIF) were examined to discard variables with VIF >10 (Netter et al., 1996). However, in the first pair of these variables, because the most significant variable absorbs most of the variance rendering related variables as nonsignificant, only BD or birth season (but not both concurrently) achieved significance.

To examine in more detail lactational differences between early- and late-born calves within the mixed group, models were analyzed separately for each of them comparing those having similar birth dates and held in groups of homogeneous age. In the case of calf gains, the model included TMY to remove the confounding effect of greater milk production in the group of mixture of calf ages.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 ACKNOWLEDGEMENTS
 REFERENCES
 
The ANOVA detected no differences in calf birth weight or hind BW among the 4 groups at the start of lactation (calf birth weight, standard births in isolation = 8.1 ± 0.2 kg, standard births of the mixed group = 8.3 ± 0.4 kg, delayed births in mixed group = 8.6 ± 0.2 kg, delayed births in isolation = 7.9 ± 0.4 kg, P > 0.1; hind BW after calving, standard births in isolation = 91.7 ± 2.8 kg, standard births of the mixed group = 99.0 ± 4.8 kg, delayed births in mixed group = 97.3 ± 3.3 kg, delayed births in isolation = 97.5 ± 3.4 kg).

Table 1Go summarized the effects of birth delay and mixture of ages. Birth delay showed a continuous effect (i.e., both between and within standard and late calving groups) reducing TMY, TPY, TFY, and TLY, which in turn resulted in decreased calf gains. Hind weight loss during lactation was also greater (P < 0.01) the later a hind calved, and the effect on increased protein content was continuous. However, fat content showed a qualitative, noncontinuous, greater (P < 0.05) percentage for delayed than for early-born calves, and a similar sharp decrease (P < 0.01) in lactose percentage.


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  		Table 1. Calf birth weight and growth rate, hind body weight change, and lactational traits of 49 hinds calving in standard (delayed 1 to 50 d; n = 18) or delayed (delayed 80 to 137 d; n = 31) birth date.
 
There seemed to be a stimulating effect on early-and late-calving hinds by mixing them together, as this increased (P < 0.05) TPY, TFY, TLY, and calf gains (Table 1Go). When models were analyzed for each calving season separately, and once corrected for the greater TMY in the mixed group, a group x BD interaction was detected for calf gains in standard, but not late-born calves [calf gain model, standard births, R2 = 76.42; sex (male vs. female) = 1.26, P = 0.027; BD = –0.11, P = 0.022; TMY = 0.032, P = 0.034; group x BD = –0.053, P = 0.009; delayed birth model, R2 = 54.78; calf birth weight = 1.89, P < 0.001; TFY = 0.35, P = 0.016]. Because no similar interaction was detected for TMY, TPY, TFY, or TLY in either standard- or late-calving hinds (models not shown), the difference in calf gain between isolated vs. mixed births at the end of the standard calving period (Figure 1Go) cannot be explained by a similar difference in production of their mothers.



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  		Figure 1. Calf gain vs. birth date in standard birth season (delayed 1 to 50 d) of calves kept with ({blacksquare}) or without ({square}) contact with calves born late (delayed 80 to 137 d). Lines show best-fit line for each population. The interaction (P < 0.01) of group x birth date showed that calf gains did not decrease at late standard dates, in the group with access to late-calving hinds. Because milk production decreased within this group, these calves presumably maintained their BW gains by suckling late-born hinds, which produce an excess of milk (Landete-Castillejos et al., 2000a). No interaction was detected in late-born calves for calf gains or hind milk production.

 
Because all deer were maintained on a similar diet and at a similar density, a greater lactation effort (i.e., greater weight loss or smaller weight gain) should be expected in the mixed vs. isolated groups. In contrast, no such effect or interaction was found (hind weight change model, standard births, R2 = 31.61; TMY = –0.042, P = 0.021; calf gain = 0.39, P = 0.055; late births model, R2 = 40.20; hind BW = –0.193, P < 0.001; calf birth weight, hind BW, TPY, TFY, TLY, BD, and group were not significant in either model).


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
ACKNOWLEDGEMENTS
 REFERENCES
 
Our results indicate a difference in lactational performance between early- and late-born hinds similar to earlier reports (Landete-Castillejos et al., 2000b; 2001; 2004a). Birth date is one of the important factors, and explains 20.8% of the variability in TPY. That is nearly twice the amount of variability explained by the next factor in effect size, hind BW, which explains 12.1%. For calf gain, and even if TPY, the milk nutrient that most influences growth (Landete-Castillejos et al. 2001, 2004b) is included in the model, birth date still explains 6.5% of the variability (vs. 33.6% for calf BW, and 13.5% for TPY). Birth date was also important in explaining variability in composition, where it explained 22.2% of the variation in percentages of fat, 6.9% in protein, and 10.3% in protein:fat ratio. The greatest effect was found for lactose, because birth date explained 60.5% of the variability. Lactose is osmotically active (Peaker, 1977; Oftedal, 1985) and is probably involved in the reduction of milk production by birth delay (explained 21.5% of the variability in milk production). Such a hypothesis is further supported by the fact that protein and fat increased in concentration, but lactose decreased, as would be expected at lower levels of milk production. On the other hand, lactose shows little variation (Landete-Castillejos et al. 2000b, 2003b), and very few factors affect its composition in addition to birth date. Experimental manipulation of diet, for example, failed to exert an effect on lactose concentration (Sutton, 1989).

Finally, birth date also affected hind weight change. Change in hind BW has been considered a measure of lactation effort (Oldham and Friggens, 1989). Thus, in previous studies, the remarkable hind weight loss was considered an attempt to maintain milk production at the expense of maternal reserves (Landete-Castillejos et al., 2000b). This hypothesis is further supported in our results because birth date explains a similar amount of variability in hind weight change as hind BW (15.2% for BD vs. 19.5% for hind BW). Lactational effort is greater in heavier hinds because more body resources generally are available for metabolism, and hind weight change is inversely related to milk production and the concentration of its nutrients (Landete-Castillejos et al., 2004b).

Our results also indicate that there seemed to be a stimulating effect on early- and late-calving hinds by mixing them together, probably as a result of increased foster suckling (allosuckling, Landete-Castillejos et al., 2000a). Because all deer were kept on a similar diet and at a similar density, a greater lactational effort (hind weight change) should be expected on the mixed vs. isolated groups. However, no such effect or interaction was found. Therefore, greater milk production was probably sustained at the expense of more grazing time. Comparing standard births in the control and mixed-age groups, calves grew less the later they were born in the control group, but not in the mixed group. Because no such interaction was found for TMY, TPY, TFY, or TLY, this sustained growth probably was not supported by milk production from their own mothers, but was probably caused by suckling early lactating, late-born hinds of the mixed group. Previous studies have shown that hinds produce an excess of milk during the first 5 wk of lactation (Landete-Castillejos et al., 2000a), precisely to counteract negative effects of these milk thefts.

In conclusion, late calving appears to produce large negative effects on lactational performance, independent of the effects of allosuckling aimed preferentially from older calves to recently calved hinds (Landete-Castillejos et al., 2000a). The mixture of birth dates appears to trigger more milk secretion and calf growth in both types of hinds that is not achieved at the expense of greater losses in hind weight. Finally, the effect of cross-suckling may sustain greater calf growth in the early-born calves in the mixed group with no growth reduction in late-born calves of the same mixed group.


   ACKNOWLEDGEMENTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ACKNOWLEDGEMENTS
REFERENCES
 
This study was supported by projects PBI-02033 (JCCM) and AGL2003-08547 (MCYT). The authors thank Maria Jesús Lorenzo for help in collecting data; Fulgencio Cebrián and Isidoro Cambronero for help in handling deer; CERSYRA for help in milk analyses; and Jeff Stevenson and 2 anonymous referees for helpful comments during peer review.

Received for publication April 29, 2004. Accepted for publication September 27, 2004.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ACKNOWLEDGEMENTS
 REFERENCES
 


Arman, P., R. N. B. Kay, E. D. Goodall, and G. A. M. Sharman. 1974. The composition and yield of milk from captive red deer (Cervus elaphus L.). J. Reprod. Fertil. 37:67–84.

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