Linear mixed-effects model fit by REML
  Data: d 
       AIC      BIC    logLik
  737.8064 771.0691 -357.9032

Random effects:
 Formula: ~1 | calf
        (Intercept) Residual
StdDev:    5.324848  1.85135

Correlation Structure: AR(1)
 Formula: ~visit_index | calf 
 Parameter estimate(s):
      Phi 
0.4160279 
Fixed effects:  weight_kg ~ diet * week + I(week^2) + room 
                     Value Std.Error  DF   t-value p-value
(Intercept)       38.54645 2.1790112 125 17.689882  0.0000
dietEnhanced       0.19987 1.9768356  27  0.101104  0.9202
week               5.40378 0.1748254 125 30.909576  0.0000
I(week^2)         -0.10741 0.0194670 125 -5.517599  0.0000
roomR2            -0.10715 2.7224800  27 -0.039356  0.9689
roomR3             2.07494 2.7224800  27  0.762152  0.4526
roomR4             3.82653 2.7224800  27  1.405531  0.1713
dietEnhanced:week  0.41318 0.1123416 125  3.677918  0.0003
 Correlation: 
                  (Intr) dtEnhn week   I(w^2) roomR2 roomR3 roomR4
dietEnhanced      -0.454                                          
week              -0.116  0.073                                   
I(week^2)          0.056  0.000 -0.891                            
roomR2            -0.625  0.000  0.000  0.000                     
roomR3            -0.625  0.000  0.000  0.000  0.500              
roomR4            -0.625  0.000  0.000  0.000  0.500  0.500       
dietEnhanced:week  0.103 -0.227 -0.321  0.000  0.000  0.000  0.000

Standardized Within-Group Residuals:
        Min          Q1         Med          Q3         Max 
-1.91591554 -0.52932423  0.08089803  0.56175374  1.99329556 

Number of Observations: 160
Number of Groups: 32 
calf = pdLogChol(1) 
            Variance  StdDev  
(Intercept) 28.354002 5.324848
Residual     3.427495 1.851350
          df      AIC
curved_ml 10 747.5685
ar1_ml    11 740.5392

 Estimate Std. Error    z Pr(>|z|)   S  2.5 % 97.5 %
     3.51       1.98 1.77   0.0762 3.7 -0.369   7.38

Term: diet
Type: response
Comparison: Enhanced - Control


Same week-8 question; changed within-calf dependence assumption.
Approximate 95% intervals concern mean differences, not individual future weights.