use strict ;
use warnings ; 

my %initial = () ;
my %seen = () ;  # increment if animal is seen 
my $new_value ; 



# Load initial values
open FILE, '<', 'file1.txt' or die 'Failed to open file1' ; 
while ( my $line = <FILE> ) { 	
	my ($animal, $count ) = split " ", $line ;
	$initial{$animal}=$count ;
	}
close FILE ;


# Open file to look for new animals
open UPDATE , '<', 'file2.txt' or die 'Failed to open file2' ; 
while ( my $line = <UPDATE> ) {
	# We assume a special pattern form your example file
	my $animal = $1 if $line =~ m/^(\w+) feed/ ;
	$seen{$animal}++ ;
	}
close UPDATE ;


# Open result file for writing
open FILE, '>','file1.txt' or die 'Failed to open file1 for writing';

foreach ( sort keys %initial) {

#Deal with the three possible case : 
#new animal, previously existing but unseen, or existing and seen

	if ( defined $seen{$_} and not defined $initial{$_} ) { 
	
			$new_value = 1
	
	} elsif (  not defined $seen{$_} and defined $initial{$_} ) { 
	
			$new_value = $initial{$_} 
	
	} else { 
			$new_value = $initial{$_} + 1  
	
	} 
	
	print FILE "$_ $new_value\n" ;
	
	
}

close FILE ;