Biology Reference
In-Depth Information
soybean meal (7.3%). Cows were fed 10 kg/cow/day during the dry period and
41 kg/cow/day during lactation.
Blood samples were collected weekly from the fifth week before parturition until
the 14th week PP for the determination of plasma concentrations of NEFA (Accorsi
et al.
2005
) and IGF-I (Leman and Kinsella
1989
; Devolder et al.
1993
). Qualitative
and quantitative characteristics of milk production were recorded for each cow. To
evaluate the PP ovarian activity, milk whey concentrations of progesterone (P4)
were determined twice per week starting from the third week after parturition
(Comin et al.
2005
).
The resumption of cyclicity was defined by the detection of three consecutive
values of P4
300 pg/mL (Comin et al.
2005
). The data obtained were analyzed
using ANOVA procedures for repeated data (mixed) and GLM of the SAS statisti-
cal package (SAS Institute
1994
). Differences were considered significant for
P
0.05.
4.3 Results
The shortened dry period resulted in a significant decrease in milk production
(26.55 vs. 27.55 kg/day,
P
0.01) without changes in fat (3.48 vs. 3.55%,
P
0.52) contents. Similarly, FCM (fat
corrected milk) and FPCM (fat/protein corrected milk) production was significantly
lower in group T than in group C (
P
0.19) or protein (3.28 vs. 3.31%,
P
¼
¼
0.01, respectively).
The NEFA profiles showed a similar trend in both groups, with increasing values
from 340 and 358
0.05 and
P
Eq/L for group T and C, respectively. The maximum values
were reached during the first week PP (957 and 908
m
Eq/L), followed by a gradual
regression to concentrations of 318 (group T) and 294
m
m
Eq/L (group C) in the last
sample (Fig. 4.3a). No significant differences (
P
0.46) were found between the
two groups regarding NEFA plasma concentrations before or after parturition.
The IGF-I in group T declined to a nadir of 8.2 ng/mL in the first week PP, and
then showed a positive trend until the end of the study (100.7 ng/mL). On the
contrary, subjects in group C showed a decline in IGF-I levels from 58.9 to 9 ng/mL
in the last weeks of pregnancy, and, after parturition, IGF-I returned to the initial
levels (56.8 ng/mL) (Fig. 4.3b). The shortening of the dry period significantly raised
the content of IGF-I in the final stages of the dry period and during early lactation
(
P
¼
0.01).
The resumption of ovarian activity, based on changes in milk whey P4, was
recorded in 10 of 13 cows with short dry periods and 9 of 12 cows with traditional
dry periods. Subjects in group T showed a significant decrease of the time interval
required for the resumption of ovarian activity as compared to cows in group C
(34.5
3.55 vs. 46.9
2.3 days,
P
0.01).
