Introduction

Sahiwal is a fabulous dairy cattle breed and renowned throughout tropical and subtropical countries due to its excellent heat and tick resistance (Bajwa et al. 2004) but its production level is much lower. Main causes are random breeding, poor nutrition, improper housing and inefficient reproductive management (Javed et al. 2002). Malnutrition is one of most important factors limiting ruminant production in developing countries (Osakwe et al. 2004; Olafadehan and Adewumi 2009). Animals in nonproductive stage (before calving) are severely neglected because of higher expenses without any visible return (Bhatti et al. 2007). The nutritional requirements of heifers become more significant during pregnancy because mammary tissue is undergoing allometric growth. The udder increases markedly in size during the fifth to sixth months of pregnancy. Prepartum maternal diet directly influences postpartum milk production and composition, and increased dietary energy enhances mammogenesis (Swanson et al. 2008). Appropriate nutritional management of replacement heifers during gestation period is indispensible for optimum mammary growth and subsequent first lactation performance in tropical herds, thereby, affecting livestock development in this agroecological zone (Maquivar et al. 2010). Although dietary energy is one of the most critical factor for production performance, very little is known about the requirements of dietary energy for pregnant heifers in tropical and subtropical areas of the world. The main objective of the present study was to determine optimum energy requirements of Sahiwal heifers during the last trimester of pregnancy and to investigate precalving of different dietary energy levels on subsequent first lactation performance.

Materials and methods

Location and climate of study area

This experiment was conducted at Livestock Experiment Station Jahangirabad, Khanewal, in the subtropical lowlands of Pakistan. Jahangirabad (30° 18′ N, 71° 56′ E) is the home of Sahiwal breed having extreme climate; very hot in summer up to 48.4°C and cold in winter down to 1°C with 93-mm average rainfall.

Animals, dietary treatments, design and feeding

Pregnant Sahiwal heifers (n = 16) at the stage of fifth to sixth months' gestation were selected and assigned to four dietary treatments (A, B, C and D) under completely randomized design experiment in which each treatment had four replicates. Isonitrogenous (CP = 14.1%) diets having varying energy, viz; A = 88%, B = 100% (Control), C = 112% and D = 124% of NRC recommended level for pregnant heifers were fed to the respective groups until calving. After calving, all heifers were fed a similar diet having CP and energy level as recommended by NRC for lactating animals. Four additional animals of the same age, weight and condition were kept as positive control and fed only ad lib green fodder under routine farm management conditions.

Data recording

Feed intake of each animal was recorded daily, whereas body weights of all pregnant heifers were determined fortnightly. Monthly body condition scoring (BCS) of animals was done by taking average individual assessment of three individuals and independently scoring the animals. The scoring method involved a manual assessment of the thickness of fat cover and prominence of bone at the tail head and loin area on a scale of 1–5: a score of 1 was extremely thin and a score of 5 was extremely fat (DEFRA 2001). Milk production was recorded daily and milk samples were collected weekly for milk composition analysis.

Digestibility trial and lab analysis

During the digestibility trial, fecal “grab” samples were taken after 2-h interval during a 24-h period. For each collection, a 50-g sample was weighed and composited to form one sample per animal. Samples were stored at −20°C till analysis. Acid insoluble ash was used as a digestibility marker (Van Keulen and Young 1977). Feed and fecal samples were analyzed for DM, N, ash contents, NDF, ADF and ADL (AOAC 2005; Van Soest et al. 1991). Milk composition analysis was carried out through Lactoscan-S Milk Analyzer (50 W, Milkotronic Ltd., Bulgaria) in WTO-Quality operation labs at UVAS, Lahore for following milk constituents: milk fat, solids not fat, milk protein, lactose and total solids.

Statistical analysis

The data were analyzed through one-way ANOVA techniques under Completely Randomized Design using SAS 9.1.3 portable software. The differences among treatment means were tested through DMRt. The mathematical model assumed was:

$$ {{\text{Y}}_{\text{ij}}} = \mu + {\tau_{\text{i}}} + {\varepsilon_{\text{ij}}} $$

where,

Y ij :

each observation on ith treatment due to jth animal

μ :

overall mean

τ i :

effect of ith treatment (∑τi = 0 and i = 1, 2, 3, 4)

ε ij :

random error associated with i th treatment and j th animal with the restriction that variance σ 2 and mean zero.

Results

Dry matter intake

The effect of precalving dietary energy levels on nutrient intake is showed in Table 1. Dry matter intake and CP intake during last 90 days of gestation was not different (p > 0.05) among treatment groups. However, values of NDF and ADF intake during prepartum period of 90 days were significantly highest in ME 88% followed by those in ME 100% and ME 112%, whereas the lowest values were recorded in ME 124%.

Table 1 Effect of different levels of energy on precalving nutrient intake in pregnant Sahiwal heifers (Mean ± SE)
Full size table

Average daily gain

The influence of precalving different dietary energy density on ADG of pregnant heifers is presented in Table 2. Heifers fed extra dietary energy (ME 112 and 124%) beyond NRC recommendations during the last trimester of pregnancy gained higher than of those fed other dietary levels, whereas ADG was also higher in ME 100% than that in ME 88%. Precalving ADG in heifers fed traditional diet (ad lib green fodder) kept under positive control group was only 300 ± 09 g/day.

Table 2 Effect of dietary energy levels on precalving average daily gain, feed efficiency, body condition score and birth weight of calves in Sahiwal 1st calf heifers (Mean ± SE)
Full size table

Feed efficiency

Feed efficiency of diets with varying dietary energy levels is mentioned in Table 2. Diets having higher energy levels than recommended by NRC (ME 112 and 124%) were similar in terms of feed efficiency. Feed efficiency of diets having ME 112 and 124% was higher than those having ME 100% and ME 88%, whereas control diet (ME 100%) was also more efficient than low energy diet having ME 88%.

Body condition score

Body condition score at the time of calving in first calf heifers fed different levels of dietary energy during the last trimester of gestation is also presented in Table 2. The BCS at calving in ME 124% was similar with that of ME 112% but higher than of that in ME 100% and ME 88%. The difference between BCS of heifers in ME 100% and ME 88% was nonsignificant, whereas BCS between ME 100% and ME 112% was also not different (P > 0.05). The BCS at calving in heifers of positive control group fed traditional diet (ad lib green fodder) during the last trimester of gestation was only 3.12 ± 0.12.

Nutrient digestibility

The effect of different dietary energy levels on digestibility of nutrients during last 90 days of gestation is mentioned in Table 3. The digestibility percentage of DM, CP, NDF and ADF was not influenced (P > 0.05) by different dietary energy levels and overall average percentages of digestibility were 69.7, 71.2, 58.5 and 52%, respectively.

Table 3 Effect of different levels of energy on precalving digestibility of nutrients in Sahiwal heifers (Mean ± SE)
Full size table

Birth weight of calf

Birth weight of calves born by first calf heifers fed different dietary energy levels during the last 90 days prepartum is given also in Table 2. Birth weight of newly born calves from first calf heifers was not different (P > 0.05) among treatment groups. The overall average birth weight in calves was 21 kg.

Milk yield

The effect of precalving dietary energy levels on daily milk yield in first calf heifers is presented in Table 4. Daily milk yield in dietary energy level (ME 100%) as per recommended by NRC was higher than other energy levels, whereas yield in ME 88% was found lower than other levels. However, milk yield was similar between ME 112% and ME 124%. The average daily milk yield in first calf heifers kept in positive control group fed precalving ad lib green fodder was only 2.56 ± 0.28 kg/day. The same pattern was observed in the case of fat-corrected milk (FCM) as shown by Table 4.

Table 4 Effect of precalving varying dietary energy levels on milk yield and its constituents in Sahiwal first calf heifers (Mean ± SE)
Full size table

Milk composition

The influence of different dietary energy levels on milk fat is mentioned in Table 4. Results depicted that provision of precalving extra dietary energy than recommended by NRC (ME 112 and 124%) significantly increased fat percentage than that of other diets having low energy level (ME 88%) and ME 100% as per recommended by NRC. The value of fat percentage in milk of heifers fed ME 100% was also found to be higher than that of ME 88%. The same pattern is seen in the case of total solids but percentages of other milk constituents, protein, lactose and solids not fat, were similar (P > 0.05) across dietary treatments as mentioned in Table 4 and their averages were 4.89, 3.85 and 9.44%, respectively.

Discussion

Dry matter intake

Similar precalving DM intake in the present study might be attributed to factors that animals under experiment were of similar age, size, weight and stage and consumed similar quantities of their respective diets because measured quantity of diets were offered daily according to body weight of animals. Similar CP intake might be attributed to experimental diets being isonitrogenous in nature. However, NDF and ADF intake were significantly maximum in ME 88% and minimum in ME 124%, whereas these were also greater in ME 100% than those in ME 112%. The pattern of NDF and ADF intake (maximum in ME 88% and minimum in ME 124%) in the present study might be attributed to similar patterns of dietary densities of these nutrients.

Results of previous studies (Dewhurst et al. 2002; Ryan et al. 2003) substantiated findings of the present study that precalving feeding management did influence prepartum total dry matter intake. However, results of McNamara et al.' (2003) study were contrary in terms that dry matter intake was higher in animals fed concentrate supplement during the last 4 weeks of gestation. The possible reasons for this contradiction might be due to different dietary treatments and higher NDF content in silage and silage straw diets that may affect dry matter intake.

Average daily gain

Improvement in precalving weight gain of heifers fed on higher dietary energy levels than recommended by NRC in the present study might be attributed to availability of surplus energy, fulfilling not only additional pregnancy requirements but also enabled heifers for their own growth. Provision of extra dietary energy during the last trimester of pregnancy becomes more significant as pregnant heifer needs extra energy for maintenance and development of fetus in her uterus (Moran 2005).

The results of the present study were strengthened by the findings of Olafadehan and Adewumi (2009) and Radunz et al. (2010) that prepartum-rich energy diet improved condition and average daily gain. However, Rabelo et al. (2003) reported differently that weight gain was not affected by precalving dietary energy treatments. The possible reason for this discrepancy might be shorter period (1 month) of precalving feeding management in that study.

Feed efficiency

The higher feed efficiency in ME 112 and 124% might be attributed to availability of surplus dietary energy enabling heifers to convert feed into live body mass more efficiently. Results of the current study were in line with the findings of Hoffman et al. (2007). Similarly, results of another study by Jenet et al. (2004) also affirmed that extra ME than recommended by NRC enhanced feed conversion efficiency in three physiological states: puberty, growth and pregnancy.

Body condition score

Improvement in body condition of heifers through ME 124% of NRC in the present study might be attributed to the factor that higher level of energy during the last trimester leads to development of extra body reserves needed in early lactation period to fulfill high demand of lactogenesis. The improvement in body condition is also corroborated by the findings of Ryan et al. (2003) and Cavestany et al. (2009) that precalving-rich energy concentrate had increased prepartum BCS even in cows. Similarly, Rabelo et al. (2003) also affirmed that precalving high energy diet improved BCS.

Nutrient digestibility

No influence of precalving dietary energy levels on digestibility of nutrients in the present study might be attributed to the best adaptability of Sahiwal pregnant heifers to utilize diets under local environment conditions and make it digestible for maintenance, growth of conceptus and growth of dam. In a previous study, Vanzant et al. (1991) also reported that organic matter digestibility was not influenced under pregnancy. However, findings of Dewhurst et al. (2000) were contrary in terms of decreased apparent rumen digestibility of nutrients during the last 6 weeks of gestation. The possible reason for this divergence might be different precalving dietary treatments.

Birth weight of calves

The similar birth weights of newly born calves in the present study might be attributed to the factor that needs of conceptus (growth of fetus, fetal membranes, uterus and mammary glands) are accorded high priority by the homeorhetic controls it transmits to the dam (Stanley 2005). No effect of prepartum dietary energy treatment on birth weight of born calves was also substantiated by findings of previous published work (Doepel et al. 2002; McNamara et al. 2003; Rabelo et al. 2003; Sanson and Coombs 2003; Olafadehan and Adewumi 2009). However, findings of Radunz et al. (2010) were contrary in nature where birth weight of calves was higher in cows fed rich energy diets prepartum. The possible reason for this divergence might be due to different precalving dietary treatment in beef cows.

Milk yield

The optimum milk production was achieved in ME 100% of NRC recommendation, whereas yield was decreased in higher dietary energy levels (ME 112 and 124%). The lesser milk yield in diets having higher energy levels than recommended by NRC might be attributed to more availability of mammary fat pad that may limit further parenchymal tissue development and, consequently, decrease milk yield during subsequent lactation (Le Cozler et al. 2008). In a previous study, Rabelo et al. (2003) reported that first calf heifers fed prepartum low energy density diet tended to have higher 3.5% FCM production than those fed higher energy density diet. However, Holtenius et al. (2003) reported discrepant results that milk yield in cows fed precalving varying dietary energy levels was similar among dietary treatments. The possible reasons for this discrepancy might be due to different breeds: Swedish black and white cows.

Milk composition

The milk fat percentage was increased by increasing precalving dietary energy level. The increase in fat content might be attributed to factor that extra dietary energy beyond NRC recommendation could have a positive effect on uptaking of milk fat precursors by mammary cells. However, other milk constituents, protein, lactose and SNF percent, were not influenced. No influence of precalving dietary energy on these milk constituents might be attributed to important homeorhetic controls of nutrients partitioning that are necessary to supply mammary needs for smooth milk synthesis.

The increase in fat content by precalving-rich energy dietary treatment was substantiated by previous studies (McNamara et al. 2003; Duske et al. 2009). Similarly, few workers (Dewhurst et al. 2002; Doepel et al. 2002; Rabelo et al. 2003) also affirmed that protein and lactose production were not affected by prepartum dietary treatments.

Conclusion

Provision of extra dietary energy during the last trimester of gestation beyond NRC (2001) recommendations for small breed pregnant heifers improved prepartum performance in terms of average daily gain, body condition and feed efficiency. However, nutrient digestibility, birth weight of calves and milk composition except fat content were not influenced with energy levels. The highest daily milk yield was observed in heifers fed ME 100% followed by ME 112, 124, and 88%. We conclude that the NRC recommendation is applicable to the subtropical regions.