The results (mean±SE) of the biochemical and haematological analysis have been presented in Table 1 and Table 2, respectively.
Table 1 reveals no significant difference (p>0.05) in the concentrations of various biochemical constituents amongst the three groups of lactating Zobawng cattle. This finding corroborates the report of
Hagawane et al., (2012). Present study further indicated that the mean concentration of blood glucose was lowest (40.67±2.04 mg dl
-1) in early stage and increased subsequently as the lactation advanced. The observed values of blood glucose for mid and late stage of lactation were 42.5±4.57 mg dl
-1 and 46.37±4.31 mgdl
-1, respectively. The trend of variations is consistent with earlier report in lactating ewes
(Roubies et al., 2006) and in lactating mares
(Heidler et al., 2002). In contrast, glucose levels were reported to be the same throughout the three stages of lactation by
Peterson and Waldern (1981); whereas,
Doornenbal et al., (1988) reported somewhat higher (p<0.05) glucose concentration at parturition that declined during lactation period. The lower level of blood glucose recorded during early stage of lactation may be ascribed to the utilization of large amount of blood glucose by mammary gland for the synthesis of lactose (
Schultz, 1968). It is reported that lactose synthesis and milk yield show a linear positive correlation with glucose uptake and thus the lactose synthesis potential is accompanied by greater glucose uptake by lactating mammary gland (
Afshar and Fathi, 2012).
The total protein level (8.45 g dl
-1) was found to be slightly higher in group-I as compared to group-II and group-III animals. This observation is contrary to the finding of
Yaylak et al., (2009), who recorded lower protein values during dry and early stages of lactation in case of Holstein cows.
Krajnicakova et al., (2003) also observed an increasing trend of total protein level of serum with the progression of lactation in lactating goats and concluded that the trend was due to the catabolism of protein for milk synthesis. The variation may be attributed to the differences in species, nutrition, husbandry, environment and methods of assay (
Beaunoyer, 1992;
Osman and Al-Busadah, 2003). However,
Hagawane et al., (2012) reported high protein value in the early stage of lactation, which is comparable to current findings. The possible explanation for this phenomenon may be the haemoconcentration and water losses due to parturition. Further, earlier investigations have clearly shown that the expression of major milk proteins increases dramatically and in a concerted way during the onset of lactation (
Bionaz and Loor, 2011).
Similarly, the mean value of blood urea nitrogen (BUN) was also recorded to be higher in initial stage of lactation and decreased as the lactation progressed. This may hold good in relation to observed apparently increased level of total protein. The BUN values observed in the present study at different stages of lactation were higher than those reported in earlier investigation
(Hagwane et al., 2012). Reinartz and Hofmann (1989) also found that serum urea concentration was significantly influenced by the lactation stage. It is recorded that the efficiency for utilization of metabolisable protein for milk production (0.68) is less than that of maintenance (1.00)
(McDonald et al., 1995). So, as the milk production increases, the overall protein utilization efficiency decreases, which consequently leads to more drainage of nitrogen in terms of urea through urine and milk
(Roy et al., 2003). An increase in urea value was further observed in the first 8 weeks of lactation (Ndibualonji and Godeau, 1993) and found to be peak at 12 weeks postpartum, which decreased slowly thereafter
(Rajcevic et al., 1993). However, other researchers found a different trend of variation in case of BUN. During the first month of lactation lower milk urea (MU) concentration was recorded by
Carlsson et al., (1995). Likewise,
Whitaker et al. (1995) also reported that cows in early lactation often have much lower MU level. In contrast, no relation was reported between urea concentration in milk and stage of lactation by
Erbersdobler et al., (1990) and values were relatively constant between 200 to 300 mg/l. Similarly,
Coustumier (1996) also found no correlation between lactation stage and urea levels except just after calving. Similar to our study,
Schepers and Meijer (1998) also observed that stage of lactation had no significant influence on BUN and thus on MU concentration. Hence, in the light of varying observations of different researchers, a systemic and critical investigation may be established in this aspect.
In this study, the drop in calcium (Ca) level (7.0±0.93 mg dl
-1) was more pronounced during early stage of lactation as compared to mid and late stage. This may be due to excessive drainage of blood calcium pool through colostrum and milk during this stage. As the stage of lactation progressed, the blood calcium level is increased, which is in agreement with the findings of
Rowlands et al., (1975) and
Nale (2003). It may be hypothesized that the cattle gradually recover from the stress of parturition and excess demand of calcium for initiation of lactation. On the contrary,
Ramakrishna (1991) recorded higher values (9.77±0.33 mg dl
-1) of calcium in lactating cattle. Further,
Yokus et al., (2004) also concluded that the levels of Ca decreased slightly in early pregnancy to late pregnancy and then increased during lactation period in sheep.
Present study also indicated that the blood creatinine level was higher in group-I as compared to group-II and group-III cows. The apparent increase in creatinine level at the early stage of lactation may be ascribed to uterine involution and myometrial protein degradation
(Bell et al., 2000). Nonetheless,
Peterson and Waldern (1981) found no differences in creatinine concentrations amongst the various stages of lactation, but observed that creatinine levels rose in dry cows with increasing days of pregnancy.
Kronfeld (1982), working with 21 Holstein herds, reported the highest serum creatinine levels during the peak of lactation. Total bilirubin concentration recorded in this study was found to be consistent throughout the lactation period indicating that its concentration remains unaffected with the stage of lactation. Similarly, no significant alteration in the concentration of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP) was recorded amongst the three groups of zobawng cows under the current study. The concentration of AST was found to be highest (72.67±6.37 U/L) in the mid lactation stage.
Ling et al., (2003) observed that the blood concentration of AST increases between day 117 and 151 of lactation (mid stage) in Holstein mares, which is in accordance with the present findings. Conversely,
Yaylak et al., (2009) reported that the stage of lactation affects AST and ALT activities significantly. An increase in ALT, AST and GGT (ã-glutamyl transferase) activity in the blood of ewes during lactation is indicative of increase in hepatic metabolism
(Antunovic et al., 2004, 2011). Further, AST and ALP are considered to be effective biomarkers to detect the energy and mineral imbalance in Saanen dairy goats
(Mundim et al., 2007). Changes in activities of these enzymes may also be related to reduced dry matter intake around parturition, which leads to hepatic lipidosis and alter the normal function of the liver
(Greenfield et al., 2000). However, no indications were found in the literature to explain the relationship of the recorded trends of variations in the concentrations of these enzymes with different stages of lactation.
Table 2 indicated that although the observed values of the haematological parameters varied apparently, the differences were statistically non significant. Similar types of observations were also recorded by
Hagawane et al., (2012). The packed cell volume (PCV), RBC count and haemoglobin (Hb) concentration was found to be lowest in Zobawng cows in early stage of lactation corroborating with those of
Esievo and Moore (1979), who concluded that the concentrations of PCV RBC, Hb along with serum iron (SI), iron binding capacity (IBC) and serum albumin decreased in early lactation and rose to pre-lactation levels by mid-lactation. Decline in the number of RBC in the blood of ewes in the early lactation was also reported by
Antunovic et al., (2011). Other haematological indices such as the TLC, DLC, mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and platelet count were found to be within the limits of normal values laid for the cattles. Similar to current investigation, non significant differences in various haematological indices were also reported by
Flores et al. (1990) during early and late stage of lactation.
